U.S. patent application number 14/090587 was filed with the patent office on 2014-03-20 for radiation exposure dose obtaining apparatus, method, and program.
This patent application is currently assigned to FUJIFILM Corporation. The applicant listed for this patent is FUJIFILM Corporation. Invention is credited to Takeshi KAMIYA, Haruyasu NAKATSUGAWA, Naoyuki NISHINO, Yasunori OHTA, Yutaka YOSHIDA.
Application Number | 20140079310 14/090587 |
Document ID | / |
Family ID | 47258804 |
Filed Date | 2014-03-20 |
United States Patent
Application |
20140079310 |
Kind Code |
A1 |
NAKATSUGAWA; Haruyasu ; et
al. |
March 20, 2014 |
RADIATION EXPOSURE DOSE OBTAINING APPARATUS, METHOD, AND
PROGRAM
Abstract
In a case where a radiation exposure dose of a subject is
obtained in a radiation exposure dose obtaining apparatus based on
a radiation image signal of each frame detected by a radiation
image detector by continuously performing radiological imaging of
the subject due to the continuous radiological imaging, an area
corresponding to a region of the subject is set in an image
represented by the radiation image signal and a radiation exposure
dose is obtained for each set area.
Inventors: |
NAKATSUGAWA; Haruyasu;
(Ashigarakami-gun, JP) ; NISHINO; Naoyuki;
(Ashigarakami-gun, JP) ; YOSHIDA; Yutaka;
(Ashigarakami-gun, JP) ; OHTA; Yasunori;
(Ashigarakami-gun, JP) ; KAMIYA; Takeshi;
(Ashigarakami-gun, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
FUJIFILM Corporation |
Tokyo |
|
JP |
|
|
Assignee: |
FUJIFILM Corporation
Tokyo
JP
|
Family ID: |
47258804 |
Appl. No.: |
14/090587 |
Filed: |
November 26, 2013 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
PCT/JP2012/003559 |
May 30, 2012 |
|
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14090587 |
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Current U.S.
Class: |
382/132 |
Current CPC
Class: |
A61B 6/487 20130101;
G06T 7/0012 20130101; A61B 6/5211 20130101; A61B 6/486 20130101;
A61B 6/542 20130101; A61B 6/481 20130101; A61B 6/469 20130101 |
Class at
Publication: |
382/132 |
International
Class: |
G06T 7/00 20060101
G06T007/00 |
Foreign Application Data
Date |
Code |
Application Number |
May 30, 2011 |
JP |
2011-120434 |
May 30, 2011 |
JP |
2011-120435 |
May 30, 2011 |
JP |
2011-120437 |
May 30, 2011 |
JP |
2011-120438 |
Claims
1. A radiation exposure dose obtaining apparatus, comprising: a
radiation exposure dose obtaining unit that obtains, based on a
radiation image signal of each frame detected by a radiation image
detector through continuous radiological imaging of a subject, a
radiation exposure dose of the subject due to the continuous
radiological imaging; and an area setting unit that sets one or
more areas corresponding to a region of the subject in an image
represented by the radiation image signal, wherein the radiation
exposure dose obtaining unit obtains the radiation exposure dose
for each area.
2. The radiation exposure dose obtaining apparatus of claim 1,
wherein the area setting unit segments the image represented by the
radiation image signal into a plurality of predetermined segmented
areas and associates each segmented area with a region of the
subject.
3. The radiation exposure dose obtaining apparatus of claim 1,
wherein the area setting unit identifies an area corresponding to a
region of the subject in the image represented by the radiation
image signal by image recognition processing and associates the
identified area with the region of the subject.
4. The radiation exposure dose obtaining apparatus of claim 1,
wherein: the apparatus comprises a contrast agent frame
identification unit that identifies a frame which includes an image
signal representing an image of a contrast agent injected into the
subject as a contrast agent frame from the radiation image signal
of each frame; and the radiation exposure dose obtaining unit
performs a correction on a radiation exposure dose for the contrast
agent frame to bring the radiation exposure dose close to an actual
value.
5. The radiation exposure dose obtaining apparatus of claim 1,
wherein the radiation exposure dose obtaining unit obtains the
radiation exposure dose based on an E.I. (Exposure Index) of the
radiation image signal.
6. A radiation exposure dose obtaining method that obtains, based
on a radiation image signal detected by a radiation image detector
through continuous radiological imaging of a subject, a radiation
exposure dose of the subject due to the continuous radiological
imaging, the method comprising the steps of: setting one or more
areas corresponding to a region of the subject in an image
represented by the radiation image signal; and obtaining the
radiation exposure dose for each area.
7. A radiation exposure dose obtaining apparatus, comprising a
radiation exposure dose obtaining unit that obtains, based on a
radiation moving picture signal, which is a collection of a
radiation image signal of each frame detected by a radiation image
detector through continuous radiological imaging of a subject, a
radiation exposure dose of the subject due to the continuous
radiological imaging, wherein the radiation exposure dose obtaining
unit calculates a signal evaluation value that serves as an index
for determining how much of radiation is detected over the entire
radiation moving picture signal by a formula (1) and obtains the
radiation exposure dose of the subject based on the signal
evaluation value of the radiation moving picture signal:
Rm=Rf.times.N (1), where: Rm: the signal evaluation value of the
radiation moving picture signal; N: the number of frames of the
entire radiation moving picture signal; and Rf: the signal
evaluation value of the radiation image signal of a predetermined
one frame in the radiation moving picture signal.
8. The radiation exposure dose obtaining apparatus of claim 7,
wherein the signal evaluation value of the radiation image signal
of a predetermined one frame is a maximum signal evaluation value
among those calculated for each radiation image signal.
9. The radiation exposure dose obtaining apparatus of claim 7,
wherein the signal evaluation value of the radiation image signal
of a predetermined one frame is a signal evaluation value of a
radiation image signal of the first frame of the radiation moving
picture signal.
10. The radiation exposure dose obtaining apparatus of claim 7,
wherein the signal evaluation value of the radiation image signal
of a predetermined one frame is a value calculated based on an E.I.
(Exposure Index).
11. A radiation exposure dose obtaining method that obtains, based
on a radiation moving picture signal, which is a collection of a
radiation image signal of each frame detected by a radiation image
detector through continuous radiological imaging of a subject, a
radiation exposure dose of the subject due to the continuous
radiological imaging, the method comprising the steps of:
calculating a signal evaluation value that serves as an index for
determining how much of radiation is detected over the entire
radiation moving picture signal by a formula (1); and obtaining the
radiation exposure dose of the subject based on the signal
evaluation value of the radiation moving picture signal:
Rm=Rf.times.N (1), where: Rm: the signal evaluation value of the
radiation moving picture signal; N: the number of frames of the
entire radiation moving picture signal; and Rf: the signal
evaluation value of the radiation image signal of a predetermined
one frame in the radiation moving picture signal.
12. A radiation exposure dose obtaining apparatus, comprising: a
radiation exposure dose obtaining unit that obtains, based on a
radiation image signal of each frame detected by a radiation image
detector through continuous radiological imaging of a subject to be
injected with a contrast agent, a radiation exposure dose of the
subject due to the continuous radiological imaging; and a contrast
agent frame identification unit that identifies a frame which
includes an image signal representing an image of the contrast
agent as a contrast agent frame from the radiation image signal of
each frame, wherein the radiation exposure dose obtaining unit
calculates a signal evaluation value of a radiation moving picture
signal, which is a collection of the radiation image signal of each
frame, by a formula (11) and obtains the radiation exposure dose of
the subject due to the continuous radiological imaging based on the
signal evaluation value of the radiation moving picture signal,
Rm-Rs.times.N/(N-M) (11) where: Rm: the signal evaluation value of
the radiation moving picture signal; N: the number of frames of the
entire radiation moving picture signal; M: the number of contrast
agent frames in the radiation moving picture signal; Rs: the sum of
signal evaluation value of radiation image signal of each frame
other than the contrast agent frame.
13. The radiation exposure dose obtaining apparatus of claim 12,
wherein the signal evaluation value of the radiation image signal
of each frame is a value calculated based on an E.I. (Exposure
Index).
14. A radiation exposure dose obtaining method that obtains, based
on a radiation image signal of each frame detected by a radiation
image detector through continuous radiological imaging of a subject
to be injected with a contrast agent, a radiation exposure dose of
the subject due to the continuous radiological imaging, the method
comprising the steps of: identifying a frame which includes an
image signal representing an image of the contrast agent as a
contrast agent frame from the radiation image signal of each frame;
calculating a signal evaluation value of a radiation moving picture
signal, which is a collection of the radiation image signal of each
frame, by a formula (11); and obtaining the radiation exposure dose
of the subject due to the continuous radiological imaging based on
the signal evaluation value of the radiation moving picture signal:
Rm=Rs.times.N/(N-M) (11) where: Rm: the signal evaluation value of
the radiation moving picture signal; N: the number of frames of the
entire radiation moving picture signal; M: the number of contrast
agent frames in the radiation moving picture signal; Rs: the sum of
signal evaluation value of radiation image signal of each frame
other than the contrast agent frame.
15. A radiation exposure dose obtaining apparatus, comprising: a
radiation exposure dose obtaining unit that obtains, based on a
radiation image signal of each frame detected by a radiation image
detector through continuous radiological imaging of a subject to be
injected with a contrast agent, a radiation exposure dose of the
subject due to the continuous radiological imaging; and a contrast
agent frame identification unit that identifies a frame which
includes an image signal representing an image of the contrast
agent as a contrast agent frame from the radiation image signal of
each frame, wherein the radiation exposure dose obtaining unit
obtains, for the radiation exposure dose of the contrast agent
frame, a value corrected by linear interpolation using a radiation
exposure value of a frame other than the contrast agent frame
adjacent to the contrast agent frame on the front side and a
radiation exposure value of a frame other than the contrast agent
frame adjacent to the contrast agent frame on the back side.
16. The radiation exposure dose obtaining apparatus of claim 15,
wherein the radiation exposure dose obtaining unit obtains, for the
radiation exposure dose of the contrast agent frame, a value
corrected by linear interpolation using a radiation exposure value
of a frame other than the contrast agent frame immediately
preceding the contrast agent frame and a radiation exposure value
of a frame other than the contrast agent frame immediately
following the contrast agent frame.
17. The radiation exposure dose obtaining apparatus of claim 15,
wherein the radiation exposure dose obtaining unit obtains the
radiation exposure dose based on an E.I. (Exposure Index) of the
radiation image signal.
18. A radiation exposure dose obtaining method that obtains, based
on a radiation image signal of each frame detected by a radiation
image detector through continuous radiological imaging of a subject
to be injected with a contrast agent, a radiation exposure dose of
the subject due to the continuous radiological imaging, the method
comprising the steps of: identifying a frame which includes an
image signal representing an image of the contrast agent as a
contrast agent frame from the radiation image signal of each frame;
and obtaining, for the radiation exposure dose of the contrast
agent frame, a value corrected by linear interpolation using a
radiation exposure value of a frame other than the contrast agent
frame adjacent to the contrast agent frame on the front side and a
radiation exposure value of a frame other than the contrast agent
frame adjacent to the contrast agent frame on the back side.
Description
TECHNICAL FIELD
[0001] The present invention relates to a radiation exposure dose
obtaining apparatus, method, and program that obtains a radiation
exposure dose of a subject to be injected with a contrast agent
based on a radiological moving picture signal which is a collection
of radiation image signals of each frame obtained through
continuous radiological imaging of the subject.
BACKGROUND ART
[0002] Recently, it has been regarded as important to manage
exposure doses of a patient due to radiological imaging in the
medical front where radiological imaging is performed. As the
relationship between the exposure dose of the patient due to
radiological imaging and a disease such as cancer is drawing
attention, it is necessary to maintain the exposure dose of a
patient due to radiological imaging and to understand and manage
the radiation exposure dose cumulatively received by the
patient.
[0003] As for the method of measuring the radiation exposure dose
received by a patient during radiological imaging, for example, a
method in which a radiation source that emits radiation is provided
with an area dosimeter and the radiation exposure dose received by
the patient is obtained based on the value measured by the
dosimeter is proposed
[0004] The employment of such method, however, requires a new
dosimeter for measuring the exposure dose of the patient, causing a
problem of cost increase.
[0005] Consequently, instead of providing such dosimeter described
above, it is proposed that the exposure dose of a patient is
obtained based on an image signal detected by a radiation image
detector that detects a radiation image of the patient (refer to,
for example, Japanese Patent No. 4387644).
DISCLOSURE OF THE INVENTION
[0006] Japanese Patent No. 4387644 proposes that an exposure dose
of a patient is obtained in the radiological imaging of a general
still image. In the actual medical front, however, radiological
imaging of moving pictures, such as fluoroscopic images, may be
performed, as well as such radiological imaging of still
images.
[0007] Further, the same radiation exposure dose may give different
amounts of impact to each region of a human body and, for example,
it is said that the impact of the same amount of radiation exposure
on the lung or stomach is two times as great as that on the liver
or esophagus. Therefore, when performing risk management of
diseases, such as cancer, more accurate management may be made by
figuring out the exposure dose of each region, in addition to the
exposure dose of the entire human body.
[0008] Japanese Patent No. 4387644 proposes neither the acquisition
of the exposure dose throughout the radiological imaging of a
fluoroscopic image nor the acquisition of the radiation exposure
dose for each region of the subject.
[0009] In the radiological imaging of such fluoroscopic images,
there may be a case where a contrast agent is injected, for
example, into a blood vessel to obtain and observe a contrast agent
image. In such a case, if the exposure dose of the patient is tried
to be obtained based simply on the image signal of the radiation
image detector, there arises a concern that the calculated value
may possibly differ from the actual exposure dose of the patient.
That is, the radiation is absorbed by the contrast agent and the
amount of radiation reached the radiation image detector is
reduced.
[0010] Further, in the case where a contrast agent is injected
during the radiological imaging of a fluoroscopic image, the
contrast agent flows through a blood vessel or the like without
remaining in one place, so that not all of the frames of the
radiological imaging of the fluoroscopic image but some of them
will include an image of the contrast agent. Therefore, it is
necessary to obtain the exposure dose of the patient throughout the
radiological imaging of the fluoroscopic image by taking into
account the point described above.
[0011] Japanese Patent No. 4387644 proposes neither the acquisition
of the exposure dose throughout the radiological imaging of a
fluoroscopic image nor the acquisition of the exposure dose
considering the inclusion of an image of a contrast agent.
[0012] In view of the circumstances described above, it is a first
object of the present invention to provide a radiation exposure
dose obtaining apparatus, method, and program capable of obtaining
a radiation exposure dose for each region of a subject when
radiological imaging of the subject is performed continuously.
[0013] It is a second, third, and fourth object of the present
invention to provide a radiation exposure dose obtaining apparatus,
method, and program capable of obtaining a radiation exposure dose
of a subject more accurately even in a case where radiological
imaging of a subject to be injected with a contrast agent is
performed in series.
[0014] A first radiation exposure dose obtaining apparatus of the
present invention includes a radiation exposure dose obtaining unit
that obtains, based on a radiation image signal of each frame
detected by a radiation image detector through continuous
radiological imaging of a subject, a radiation exposure dose of the
subject due to the continuous radiological imaging and an area
setting unit that sets one or more areas corresponding to a region
of the subject in an image represented by the radiation image
signal, in which the radiation exposure dose obtaining unit obtains
the radiation exposure dose for each area.
[0015] In the radiation exposure dose obtaining apparatus described
above, the area setting unit may segment the image represented by
the radiation image signal into a plurality of predetermined
segmented areas and associate each segmented area with a region of
the subject or may identify an area corresponding to a region of
the subject in the image represented by the radiation image signal
by image recognition processing and associate the identified area
with the region of the subject.
[0016] The object of the first radiation exposure dose obtaining
apparatus described above is to measure and manage an exposure dose
for each region (organ) as the radiation absorption coefficient and
the allowable cumulative dose differ from region (organ) to region
(organ).
[0017] Because there is a concern that children are more influenced
by radiation exposure than adults, it is important to measure and
manage the exposure dose more accurately. Bodies of children grow
remarkably and the size of an organ in an image is likely to be
changed with time even if the radiological imaging is performed
under the same condition. Further, even for radiological imaging of
an adult, the size of an organ in images may possibly be changed
due to difference in radiological imaging equipment or imaging
condition. Therefore, an area is set in association with a region
means that the area may be variable for each imaging.
[0018] In the radiation exposure dose obtaining apparatus described
above, there may be a case, for example, where a contrast agent is
injected into a blood vessel or the like to obtain and observe a
contrast agent image of the blood vessel or the like. In such a
case, if an exposure dose of the subject is obtained based simply
on an image signal of the radiation image detector, an accurate
exposure dose cannot be obtained. That is, the radiation applied to
the patient is absorbed by the contrast agent, as well as the body,
before reaching the radiation image detector. Consequently, the
exposure dose obtained based on the radiation image signal which
reflects such absorption of the radiation by the contrast agent is
not accurate.
[0019] Further, in the case where a contrast agent is injected for
radiological imaging of a fluoroscopic image, the contrast agent
flows through a blood vessel or the like without remaining in one
place, so that not all of the frames of the radiological imaging of
the fluoroscopic image but some of them will capture an image of
the contrast agent. Therefore, it is preferable that the exposure
dose of the patient over the throughout the imaging of the
fluoroscopic image is obtained by taking into account the point
described above.
[0020] Therefore, it is preferable that the radiation exposure dose
obtaining apparatus described above includes a contrast agent frame
identification unit that identifies a frame which includes an image
signal representing an image of a contrast agent injected into the
subject as a contrast agent frame from the radiation image signal
of each frame and the radiation exposure dose obtaining unit
performs a correction on a radiation exposure dose for the contrast
agent frame to bring the radiation exposure dose close to an actual
value.
[0021] Preferably, the radiation exposure dose obtaining unit
obtains the radiation exposure dose based on an E.I. (Exposure
Index) of the radiation image signal, but any value other than this
may also be used as long as it serves as an index for determining
how much of radiation is detected in each frame, such as an average
value of signal values in each frame or a value calculated by
considering the histogram. The "value calculated based on an E.I."
as used herein may be the value of the E.I. itself or a value
obtained by making a certain correction to the E.I.
[0022] A first radiation exposure dose obtaining method of the
present invention obtains, based on a radiation image signal
detected by a radiation image detector through continuous
radiological imaging of a subject, a radiation exposure dose of the
subject due to the continuous radiological imaging, comprising the
steps of: setting one or more areas corresponding to a region of
the subject in an image represented by the radiation image signal;
and obtaining the radiation exposure dose for each area.
[0023] The radiation exposure dose obtaining method described above
may be provided as a program for causing a computer to perform the
method.
[0024] A second radiation exposure dose obtaining apparatus of the
present invention includes a radiation exposure dose obtaining unit
that obtains, based on a radiation moving picture signal, which is
a collection of a radiation image signal of each frame detected by
a radiation image detector through continuous radiological imaging
of a subject, a radiation exposure dose of the subject due to the
continuous radiological imaging, in which the radiation exposure
dose obtaining unit calculates a signal evaluation value that
serves as an index for determining how much of radiation is
detected over the entire radiation moving picture signal by a
formula (1) and obtains the radiation exposure dose of the subject
based on the signal evaluation value of the radiation moving
picture signal:
Rm=Rf.times.N (1).
[0025] A second radiation exposure dose obtaining method of the
present invention obtains, based on a radiation moving picture
signal, which is a collection of a radiation image signal of each
frame detected by a radiation image detector through continuous
radiological imaging of a subject, a radiation exposure dose of the
subject due to the continuous radiological imaging, the method
including the steps of: calculating a signal evaluation value that
serves as an index for determining how much of radiation is
detected over the entire radiation moving picture signal by a
formula (1); and obtaining the radiation exposure dose of the
subject based on the signal evaluation value of the radiation
moving picture signal:
Rm=Rf.times.N (1).
[0026] In the radiation exposure dose obtaining apparatus and
method described above, the following have the following
meanings:
[0027] Rm: the signal evaluation value of the radiation moving
picture signal;
[0028] N: the number of frames of the entire radiation moving
picture signal; and
[0029] Rf: the signal evaluation value of the radiation image
signal of a predetermined one frame in the radiation moving picture
signal.
[0030] The formula (1) given above will now be described in detail.
The signal evaluation value of the radiation moving picture signal
is a value that serves as an index for determining how much of
radiation is detected over the entire radiation moving picture
signal, and the signal evaluation value is calculated based on a
signal evaluation value of radiation image signals of predetermined
one frame (a value that serves as an index for determining how much
of radiation is detected in the predetermined one frame).
[0031] The "signal evaluation value of radiation image signals of
predetermined one frame" is preferable to be a maximum signal
evaluation value among those calculated for each radiation image
signal or a signal evaluation value of radiation image signals of
the first frame of the radiation moving picture signal, but any
other form of may be employed as long as it is a signal evaluation
value of radiation image signals for one frame deemed to be free of
error factor, such as a signal evaluation value of radiation image
signals of one particular frame which does not include any error
factor such as the contrast agent described above, an average value
of signal evaluation values of radiation image signals of a
plurality of frames that do not include any error factor, or the
like.
[0032] The signal evaluation value of radiation image signals of a
predetermined one frame is preferable to be a value calculated
based on an E.I. (Exposure Index), but any value other than this
may also be used as long as it serves as an index for determining
how much of radiation is detected in each frame, such as an average
value of signal values in each frame or a value calculated by
considering the histogram. The "value calculated based on an E.I."
as used herein may be the value of the E.I. itself or a value
obtained by making a certain correction to the E.I.
[0033] The radiation exposure dose obtaining method described above
may be provided as a program for causing a computer to perform the
method.
[0034] A third radiation exposure dose obtaining apparatus of the
present invention includes: a radiation exposure dose obtaining
unit that obtains, based on a radiation image signal of each frame
detected by a radiation image detector through continuous
radiological imaging of a subject to be injected with a contrast
agent, a radiation exposure dose of the subject due to the
continuous radiological imaging; and a contrast agent frame
identification unit that identifies a frame which includes an image
signal representing an image of the contrast agent as a contrast
agent frame from the radiation image signal of each frame, in which
the radiation exposure dose obtaining unit calculates a signal
evaluation value of a radiation moving picture signal, which is a
collection of the radiation image signal of each frame, by a
formula (11) and obtains the radiation exposure dose of the subject
due to the continuous radiological imaging based on the signal
evaluation value of the radiation moving picture signal:
Rm=Rs.times.N/(N-M) (11).
[0035] A third radiation exposure dose obtaining method of the
present invention obtains, based on a radiation image signal of
each frame detected by a radiation image detector through
continuous radiological imaging of a subject to be injected with a
contrast agent, a radiation exposure dose of the subject due to the
continuous radiological imaging, the method comprising the steps
of: identifying a frame which includes an image signal representing
an image of the contrast agent as a contrast agent frame from the
radiation image signal of each frame; calculating a signal
evaluation value of a radiation moving picture signal, which is a
collection of the radiation image signal of each frame, by a
formula (11); and obtaining the radiation exposure dose of the
subject due to the continuous radiological imaging based on the
signal evaluation value of the radiation moving picture signal:
Rm=Rs.times.N/(N-M) (11).
[0036] In the radiation exposure dose obtaining apparatus and
method described, above, the following have the following
meanings:
[0037] Rm: the signal evaluation value of the radiation moving
picture signal;
[0038] N: the number of frames of the entire radiation moving
picture signal;
[0039] M: the number of contrast agent frames in the radiation
moving picture signal;
[0040] Rs: the sum of signal evaluation value of radiation image
signal of each frame other than the contrast agent frame.
[0041] The formula (11) given above will now be described in
detail. The signal evaluation value of the radiation moving picture
signal is a value that serves as an index for determining how much
of radiation is detected over the entire radiation moving picture
signal, and the signal evaluation value is calculated based on a
signal evaluation value of radiation image signals of each frame (a
value that serves as an index for determining how much of radiation
is detected in each frame).
[0042] The signal evaluation value of radiation image signals of
each frame is preferable to be a value calculated based on an E.I.
(Exposure Index), but any value other than this may also be used as
long as it serves as an index for determining how much of radiation
is detected in each frame, such as an average value of signal
values in each frame or a value calculated by considering the
histogram. The "value calculated based on an E.I." as used herein
may be the value of the E.I. itself or a value obtained by making a
certain correction to the E.I.
[0043] Further, an average value Ra of signal evaluation values of
radiation image signals of each frame other than a contrast agent
frame in the radiation moving picture signal may be obtained as in
a formula (12), so that the formula (11) may be expressed as a
formula (13).
Ra=Rs/(N-M) (12)
Rm=Ra.times.N (13)
[0044] The radiation exposure dose obtaining method described above
may be provided as a program for causing a computer to perform the
method.
[0045] A fourth radiation exposure dose obtaining apparatus of the
present invention includes: a radiation exposure dose obtaining
unit that obtains, based on a radiation image signal of each frame
detected by a radiation image detector through continuous
radiological imaging of a subject to be injected with a contrast
agent, a radiation exposure dose of the subject due to the
continuous radiological imaging; and a contrast agent frame
identification unit that identifies a frame which includes an image
signal representing an image of the contrast agent as a contrast
agent frame from the radiation image signal of each frame, in which
the radiation exposure dose obtaining unit obtains, for the
radiation exposure dose of the contrast agent frame, a value
corrected by linear interpolation using a radiation exposure value
of a frame other than the contrast agent frame adjacent to the
contrast agent frame on the front side and a radiation exposure
value of a frame other than the contrast agent frame adjacent to
the contrast agent frame on the back side.
[0046] A fourth radiation exposure dose obtaining method of the
present invention obtains, based on a radiation image signal of
each frame detected by a radiation image through continuous
radiological imaging of a subject to be injected with a contrast
agent, the method comprising the steps of : identifying a frame
which includes an image signal representing an image of the
contrast agent as a contrast agent frame from the radiation image
signal of each frame; and obtaining, for the radiation exposure
dose of the contrast agent frame, a value corrected by linear
interpolation using a radiation exposure value of a frame other
than the contrast agent frame adjacent to the contrast agent frame
on the front side and a radiation exposure value of a frame other
than the contrast agent frame adjacent to the contrast agent frame
on the back side.
[0047] In the radiation exposure dose obtaining apparatus and
method described above, the term "a frame other than the contrast
agent frame adjacent to the contrast agent frame on the front side"
as used herein refers to a frame within a several frames before and
after a frame other than the contrast agent frame immediately
preceding the contrast agent frame as the reference, and the term
"a frame other than the contrast agent frame adjacent to the
contrast agent frame on the back side" as used herein refers to a
frame within a several frames before and after a frame other than
the contrast agent frame immediately following the contrast agent
frame as the reference.
[0048] In the radiation exposure dose obtaining apparatus and
method described above, a sufficient correction effect may be
obtained by a correction through linear interpolation using a frame
other than a contrast agent frame immediately preceding the
contrast agent frame and a frame other than the contrast agent
frame immediately following the contrast agent frame. In the case
where the identification accuracy is not perfect, in view of the
frame rate at the time of imaging, contrast agent frame
identification method, and actual imaging state the frame to be
used by the linear interpolation may be changed from the frame at
the reference position (immediately preceding or following the
contrast agent frame) to a frame within a several frames before or
after the frame at the reference position.
[0049] For example, in the case where a method in which a frame
obtained during injection of a contrast agent is identified as a
contrast agent frame, the contrast agent may possibly remain in the
human body for a while after the injection of the contrast agent is
ended. Thus, the frame on the back side of the contrast agent frame
used for the linear interpolation may be changed to a frame further
on the back side by the number of frames corresponding to the
residual time with reference to the frame other than the contrast
agent frame immediately following the contrast agent frame.
[0050] It is preferable that the radiation exposure dose is
obtained based on an E.I. (Exposure Index) of the radiation image
signal, but any value other than this may also be used as long as
it serves as an index for determining how much of radiation is
detected in each frame, such as an average value of signal values
in each frame, a value calculated by considering the histogram, or
the like. The value calculated based on the E.I. may be the value
of E.I. itself or a value obtained by making a certain correction
to the E.I.
[0051] The radiation exposure dose obtaining method described above
may be provided as a program for causing a computer to perform the
method.
[0052] According to the first radiation exposure dose obtaining
apparatus, method, and program of the present invention, in the
case where a radiation exposure dose of a subject is obtained,
based on a radiation image signal of each frame detected by a
radiation image detector through continuous radiological imaging of
the subject, due to the continuous radiological imaging, an area or
areas corresponding to a region of the subject is set in an image
represented by the radiation image signal and the radiation
exposure dose is obtained for each set area. In the case where
disease risk management is performed for a patient, this allows
more appropriate management considering different influences of
radiation for each region of the body.
[0053] If an arrangement is adopted in which a frame which includes
an image signal representing an image of a contrast agent injected
into the subject as a contrast agent frame from the radiation image
signal of each frame, and a correction is performed on a radiation
exposure dose for the contrast agent frame to bring the radiation
exposure dose close to an actual value, a more accurate radiation
exposure dose of the subject may be obtained.
[0054] Further, if the radiation exposure dose is obtained based on
an E.I. (Exposure Index) of the radiation image signal, the value
may reflect the actual radiation exposure dose of the subject and a
further accurate radiation exposure dose may be obtained.
[0055] According to the second radiation exposure dose obtaining
apparatus, method, and program of the present invention, in the
case where a radiation exposure dose of a subject is obtained,
based on a radiation moving picture signal, which is a collection
of a radiation image signal of each frame detected by a radiation
image detector through continuous radiological imaging of the
subject, a radiation exposure dose of the subject due to the
continuous radiological imaging, a signal evaluation value that
serves as an index for determining how much of radiation is
detected over the entire radiation moving picture signal is
calculated by a formula (1) capable of performing the calculation
without using information of a frame which includes an error factor
and a radiation exposure dose of the subject throughout the
continuous radiological imaging is obtained based on the calculated
signal evaluation value of the radiation moving picture signal.
This allows an accurate radiation exposure dose to be obtained.
Further, this requires only a simple calculation and the processing
load may be reduced.
Rm=Rf.times.N (1)
[0056] Further, the use of a maximum signal evaluation value among
those calculated for each radiation image signal as the signal
evaluation value of the radiation image signal of a predetermined
frame may eliminate the concern that the radiation exposure dose of
the subject is underestimated.
[0057] Further, as it is often the case that an error factor in
obtaining a radiation exposure dose, such as contrast agent
injection into a subject and the like, is not generally included
right after the start of application of radiation to a subject, so
that if the signal evaluation value of the radiation image signal
of the first frame of the radiation moving picture signal is used
as the signal evaluation value, a frame deemed not to include an
error factor may be identified easily.
[0058] Further, if a value calculated based on an E.I. (Exposure
Index) is used as the signal evaluation value of radiation image
signal of a predetermined one frame, the value may reflect the
actual radiation exposure dose of the subject and a further
accurate radiation exposure dose may be obtained.
[0059] According to the third radiation exposure dose obtaining
apparatus, method, and program of the present invention, in the
case where a radiation exposure dose of a subject to be injected
with a contrast agent is obtained, based on a radiation image
signal of each frame detected by a radiation image detector through
continuous radiological imaging of the subject, a radiation
exposure dose of the subject due to the continuous radiological
imaging, a frame which includes an image signal representing an
image of the contrast agent as a contrast agent frame from the
radiation image signal of each frame, a signal evaluation value of
a radiation moving picture image, which is a collection of the
radiation image signal of each frame, is calculated by a formula
(11) that dose not use information of a contrast agent frame, and a
radiation exposure dose of the subject throughout the continuous
radiological imaging is obtained based on the calculated signal
evaluation value of the radiation moving picture signal. This
allows a more accurate radiation expose dose of the subject which
takes into account the inclusion of an image of a contrast agent in
the radiation image to be obtained.
Rm=Rs.times.N/(N-M) (11)
[0060] Further, if a value calculated based on an E.I. (Exposure
Index) is used as a signal evaluation value of the radiation image
signal of each frame required for the calculation of the formula
(11), the value may reflect the actual radiation exposure dose of
the subject and a further accurate radiation exposure dose may be
obtained.
[0061] According to the fourth radiation exposure dose obtaining
apparatus, method, and program of the present invention, in the
case where a radiation exposure dose of a subject to be injected
with a contrast agent is obtained, based on a radiation image
signal of each frame detected by a radiation image detector through
continuous radiological imaging of the subject, a radiation
exposure dose of the subject due to the continuous radiological
imaging, a frame which includes an image signal representing an
image of the contrast agent is identified as a contrast agent frame
from the radiation image signal of each frame and, for the
radiation exposure dose of the contrast agent frame, a value
corrected by linear interpolation using a radiation exposure value
of a frame other than the contrast agent frame adjacent to the
contrast agent frame on the front side and a radiation exposure
value of a frame other than the contrast agent frame adjacent to
the contrast agent frame on the back side is used. This allows a
more accurate radiation expose dose of the subject which takes into
account the inclusion of an image of a contrast agent in the
radiation image to be obtained.
[0062] Further, if a radiation exposure dose is obtained based on
an E.I. (Exposure Index) of radiation image signal, the value may
reflect the actual radiation exposure dose of the subject and a
further accurate radiation exposure dose may be obtained.
BRIEF DESCRIPTION OF DRAWINGS
[0063] FIG. 1 is a block diagram of a radiation image capturing
system that uses an embodiment of a first radiation exposure dose
obtaining apparatus of the present invention, illustrating an
overall schematic configuration thereof.
[0064] FIG. 2 is a flowchart illustrating an operation of the
radiation image capturing system that uses an embodiment of the
radiation exposure dose obtaining apparatus described above.
[0065] FIG. 3 is a drawing for explaining an example radiation
image and a region setting procedure (1).
[0066] FIG. 4 illustrates a variation in the radiation exposure
dose for each region.
[0067] FIG. 5 is a drawing for explaining an example radiation
image and a region setting procedure (2).
[0068] FIG. 6 illustrates the DICOM saving format.
[0069] FIG. 7 is a block diagram of a radiation image capturing
system that uses an embodiment of a second radiation exposure dose
obtaining apparatus of the present invention, illustrating an
overall schematic configuration thereof.
[0070] FIG. 8 is a flowchart illustrating an operation of the
radiation image capturing system that uses an embodiment of the
radiation exposure dose obtaining apparatus described above.
[0071] FIG. 9 shows a timing chart illustrating the relationship
among the radiation emission timing, charge accumulation timing in
a radiation image detector, and contrast agent detection signal,
and a graph representing radiation exposure doses calculated based
on radiation image signal of each frame.
[0072] FIG. 10 is a block diagram of a radiation image capturing
system that uses an embodiment of a third radiation exposure dose
obtaining apparatus of the present invention, illustrating an
overall schematic configuration thereof.
[0073] FIG. 11 is a flowchart illustrating an operation of the
radiation image capturing system that uses an embodiment of the
radiation exposure dose obtaining apparatus described above.
[0074] FIG. 12 shows a timing chart illustrating the relationship
among the radiation emission timing, charge accumulation timing in
a radiation image detector, and contrast agent detection signal,
and a graph representing radiation exposure doses calculated based
on a radiation image signals of each frame.
[0075] FIG. 13 is a block diagram of a radiation image capturing
system that uses an embodiment of a fourth radiation exposure dose
obtaining apparatus of the present invention, illustrating an
overall schematic configuration thereof.
[0076] FIG. 14 is a flowchart illustrating an operation of the
radiation image capturing system that uses an embodiment of the
radiation exposure dose obtaining apparatus described above.
[0077] FIG. 15 shows a timing chart illustrating the relationship
among the radiation emission timing, charge accumulation timing in
a radiation image detector, and contrast agent detection signal,
and a graph representing radiation exposure doses calculated based
on radiation image signals of each frame.
BEST MODE FOR CARRYING OUT THE INVENTION
[0078] Hereinafter, an embodiment of a radiation image capturing
system that uses an embodiment of the first radiation exposure dose
obtaining apparatus of the present invention will be described with
reference to the accompanying drawings. FIG. 1 is a block diagram
of the radiation image capturing system of the present embodiment,
illustrating an overall schematic configuration thereof.
[0079] As illustrated in FIG. 1, the radiation image capturing
system of the present embodiment includes a radiation image
capturing apparatus 10 that captures a fluoroscopic image (moving
picture) of a patient, a radiation image display apparatus 20 that
displays the fluoroscopic image captured by the radiation image
capturing apparatus 10, a contrast agent injection apparatus 30
that injects a contrast agent into a blood vessel or a lymph vessel
of the patient, a radiation exposure dose obtaining apparatus 40
that obtains an exposure dose of the patient based on an image
signal of the fluoroscopic image captured by the radiation image
capturing apparatus 10, a radiation exposure dose management
apparatus 50 that stores and manages the exposure dose of each
patient obtained by the radiation exposure dose obtaining apparatus
40, and a system control apparatus 60 that performs overall control
of the radiation image capturing system.
[0080] As illustrated in FIG. 1, the radiation image capturing
apparatus 10 includes a radiation application unit 11 that has an
X-ray tube, an aperture stop, and the like and applies radiation
emitted from the x-ray tube and passed through the aperture stop to
a patient, a radiation image detector 12 that detects radiation
transmitted through the patient and outputs a radiation image
signal representing a radiation image of the patient, a radiation
image storage unit 13 that stores the radiation image signal
outputted from the radiation image detector 12, and a control unit
14 that performs overall control of the radiation image capturing
apparatus 10.
[0081] The radiation image detector 12 allows repeated use for
recording and reading of radiation images, and a so-called direct
type radiation image detector that records a radiation image by
generating and accumulating a charge by directly receiving
radiation or a so-called indirect type radiation image detector
that records a radiation image by converting radiation first to
visible light and then converting the visible light to a charge and
accumulating the charge may be used. As for the radiation image
signal reading method for reading out the radiation image recorded
by accumulating charges in the manner described above, a so-called
TFT (thin film transistor) reading method in which a radiation
image signal is read by ON/OFF switching thin film transistors and
a so-called optical reading method in which a radiation image
signal is read out by applying reading light are preferably used,
but others may also be used.
[0082] The radiation image capturing apparatus 10 is used to
capture a fluoroscopic image (moving picture) of a subject to be
injected with a contrast agent by the contrast agent injection
apparatus 30, and the control unit 14 controls the radiation
application unit 11 and radiation image detector 12 such that the
fluoroscopid image is captured. More specifically, the control unit
14 controls the radiation application unit 11 to apply radiation at
a predetermined frame rate and the radiation image detector 12 to
perform recording and reading of a radiation image by the
application of the radiation. Then, the radiation image signal of
each frame outputted from the radiation image detector 12 is
sequentially stored in the radiation image storage unit 13.
Further, the control unit 14 of the present embodiment appends
information indicating whether or not an image signal representing
an image of the contrast agent is included in the radiation image
signal of each frame when storing the radiation image signal of
each frame in the radiation image storage unit 13, the operation of
which will be described later in detail.
[0083] As for the structure of the radiation image capturing
apparatus 10, a structure in which image capturing is performed
with the patient being in the upright position or in the lateral
position may be employed. Further, a structure that allows image
capturing with the patient being both in upright position and
lateral position may be employed.
[0084] The radiation image display apparatus 20 generates a display
control signal by performing predetermined processing on the
radiation image signal of each frame read out from the radiation
image storage unit 13 of the radiation image capturing apparatus 10
and displays a fluoroscopic image of the patient on the monitor
based on the display control signal.
[0085] The contrast agent injection apparatus 30 automatically
injects a contrast agent into a patient based on an instruction
input from the user or based on a preset injection start timing of
the contrast agent. More specifically, the contrast agent injection
apparatus 30 includes a contrast agent injection unit 31 formed of,
for example, a syringe and injects a contrast agent into a blood
vessel of the patient or the like, an injection drive unit 32 which
drives the injection operation of the contrast agent injection unit
31, a control unit 33 that controls the operation of the injection
drive unit 32, and a contrast agent injection detection sensor unit
34 that detects whether or not the contrast agent is being injected
into a blood vessel or the like of the patient from the contrast
agent injection apparatus 30.
[0086] The injection drive unit 32 moves, for example, the piston
of the syringe of the contrast agent injection unit 31 and is
formed of a power means, such as an air pressure, motor, or
hydraulic pressure.
[0087] The contrast agent injection detection sensor unit 34
includes a sensor for detecting that the contrast agent is
discharged from the contrast agent injection unit 31. Then, the
contrast agent injection detection sensor unit 34 outputs a
contrast agent detection signal to the control unit 14 of the
radiation image capturing apparatus 10.
[0088] The radiation exposure dose obtaining apparatus 40 includes
an area setting unit 41 that sets one or more areas corresponding
to a body region or regions of a patient in an image represented by
the radiation image signals of each frame read out from the
radiation image storage unit 13 of the radiation image capturing
apparatus 10, a contrast agent frame identification unit 42 that
identifies a radiation image signal of a frame that includes an
image signal of an image of a contrast agent as a contrast agent
frame from the radiation image signal of each frame, and a
radiation exposure dose obtaining unit 43 that obtains a radiation
exposure dose of the patient for each region set by the area
setting unit 41 based on the radiation image signals of each frame.
Operations of the area setting unit 41, the contrast agent frame
identification unit 42, and the radiation exposure dose obtaining
unit 43 will be described later in detail.
[0089] The radiation exposure dose management apparatus 50 stores
the radiation exposure dose obtained by the radiation exposure dose
obtaining apparatus 40 and manages the radiation exposure dose of
each patient.
[0090] The system control apparatus 60 outputs control signals to
the radiation image capturing apparatus 10, the radiation image
display apparatus 20, the contrast agent injection apparatus 30,
the radiation exposure dose obtaining apparatus 40, and the
radiation exposure dose management apparatus 50 to control the
operations thereof and at the same time performs input/output
signal control between these apparatuses. The system control
apparatus 60 is provided with an input unit 70 which receives an
instruction input and other inputs, such as image capturing
conditions, patient ID information and the like, from the user. The
input information received at the input unit 70 is outputted to
each apparatus by the system control apparatus 60 as required.
[0091] An operation of the radiation image capturing system of the
present embodiment will now be described with reference to the
flowchart of FIG. 2.
[0092] First, a patient, the subject of the image capturing, is
placed on an image capturing platform or the like provided in the
radiation image capturing apparatus 10 and the patient is put into
position (S10).
[0093] Then, ID information of the image capturing target patient
and an image capturing condition are inputted by the user using the
input unit 70 and the patient ID information is registered in the
radiation exposure dose management apparatus 50 while the image
capturing condition is set to the control unit 14 of the radiation
image capturing apparatus 10 (S12). The image capturing condition
may include a tube voltage, tube current, and application time in
order to apply an appropriate dose of radiation to an image
capturing region of the patient, as well as a frame rate for
capturing a fluoroscopic image. As for the frame rate for capturing
the fluoroscopic image, for example, a frame rate of 5 fps to 60
fps is set.
[0094] Next, an instruction to start fluoroscopic image capturing
of the patient is inputted by the user using the input unit 70 and
in response to the input, a control signal is outputted from the
system control apparatus 60 to the radiation image capturing
apparatus 10 to capture a fluoroscopic image, and the radiation
image capturing apparatus 10 starts fluoroscopic image capturing
according to the inputted control signal (S14).
[0095] More specifically, the X-ray tube of the radiation
application unit 11 is controlled based on the inputted imaging
condition and a predetermined dose of radiation is applied toward
the patient intermittently at a predetermined frame rate.
[0096] Then, radiation transmitted through the patient is applied
to the radiation image detector 12 and subjected to a
photoelectrical conversion in the radiation image detector 12 and
accumulated therein as a charge signal.
[0097] Thereafter, each time the application of radiation for each
frame is ended, the charge signal accumulated in the radiation
image detector 12 is read out by the control unit 14, then
converted to a digital signal by an A/D converter (not shown), and
stored in the radiation image storage unit 13.
[0098] Then, the radiation image signal of each frame stored in the
radiation image storage apparatus 13 is sequentially read out and
outputted to the radiation image display apparatus 20. The
radiation image display apparatus 20 sequentially generates a
display control signal based on the inputted radiation image signal
of each frame and sequentially outputs the display control signal
to the monitor to display a fluoroscopic image of the patient as a
moving picture (S16). It is assumed here that the radiation image
signal of each frame stored in the radiation image storage unit 13
will remain un-erased in the radiation image storage unit 13 after
being read out.
[0099] Here, if the user desires to observe a contrast agent image,
such as a blood vessel or the like, while the fluoroscopic image
capturing and display are performed in the manner described above,
a contrast agent injection instruction is inputted using the input
unit 70 (S18).
[0100] When the contrast agent injection instruction is inputted at
the input unit 70, a control signal is outputted from the system
control apparatus 60 to the contrast agent injection apparatus 30.
The contrast agent injection apparatus 30 starts contrast agent
injection based on the inputted control signal. More specifically,
the contrast agent injection unit 31 is driven by the injection
drive unit 32 and a predetermined amount of contrast agent is
discharged from the contrast agent injection unit 31.
[0101] Here, the contrast agent injection detection sensor unit 34
provided in the contrast agent injection apparatus 30 detects that
the contrast agent is discharged and a detection signal is
outputted to the control unit 14 of the radiation image capturing
apparatus 10 (S20). When the contrast agent detection signal is
inputted, the control unit 14 of the radiation image capturing
apparatus 10 appends to a radiation image signal of a frame
captured while the contrast agent detection signal is inputted
information indicating that it includes an image signal
representing an image of the contrast agent (hereinafter, referred
to as "contrast agent frame information") as header information,
and stores the radiation image signal in the radiation image
storage unit 13 with the header information (S22).
[0102] Then, the radiation image signals captured while the
contrast agent is injected are also read out from the radiation
image storage unit 13 and sequentially outputted to the radiation
image display apparatus 20. The radiation image display apparatus
20 sequentially generates display control signals based on the
inputted radiation image signals, and displays radiation images
including a contrast agent image on the monitor based on the
display control signals (S24).
[0103] Then, after the discharge of the predetermined amount of
contrast agent from the contrast agent injection apparatus 30 is
completed and the contrast agent detection signal is not detected
any more in the contrast agent injection detection sensor unit 34,
radiation image signals captured are stored in the radiation image
storage unit 13 without the contrast agent frame information being
appended, and the radiation image signal of each frame is read out
from the radiation image storage unit 13 in the manner described
above and a fluoroscopic image is displayed on the radiation image
display apparatus 20.
[0104] Thereafter, when an instruction to end the fluoroscopic
image capturing is inputted by the user through the input unit 70,
the system control apparatus 60 outputs a control signal to the
radiation image capturing apparatus 10 to end the fluoroscopic
image capturing, and the radiation image capturing apparatus 10
ends the fluoroscopic image capturing in response to the inputted
control signal (S26).
[0105] When the fluoroscopic image capturing described above is
ended, the system control apparatus 60 reads out radiation image
signals of all frames stored in the radiation image storage unit 13
of the radiation image capturing apparatus 10 and inputs the
radiation image signals to the radiation exposure dose obtaining
apparatus 40.
[0106] Then, first, the area setting unit 41 sets a region in an
image represented by the radiation image signal of each frame
corresponding to a body region of the patient (S28). More
specifically, the image represented by the radiation image signal
is segmented into 9 segmented areas in square mesh, as illustrated
in FIG. 3, and each segmented area is associated with a body region
of the patient. If the image shown in FIG. 3 is taken as an
example, the division is made such that the segmented areas 1 to 6
are categorized as the chest region and segmented areas 7 to 9 are
categorized as the lumbar region.
[0107] As for the method of associating each segmented area with a
body region of the patient, a method in which an association
instruction is received from the user to arbitrarily associate each
segmented area with a body region of the patient or a method in
which each segmented area is automatically associated with a body
region of the patient based on the information, such as the patient
ID information, imaged region, image capturing conditions, may be
used. Further, the size, shape, and the number of the segmented
areas are not limited to those described above and, for example, in
the case where a strict management is required, the size of the
segmented areas may be reduced while the number of the segmented
areas may be increased.
[0108] Further, instead of segmenting the image represented by the
radiation image signal into a plurality of segmented areas in
advance, an area corresponding to a region of the subject is
directly identified in the image represented by the radiation image
signal using a known image recognition technology and the
identified region may be associated with a region of the subject.
By way of example, in the case of the image shown in FIG. 5, an
area Ac and an area A1 corresponding respectively to the chest
region and the lumbar region of the subject are identified in the
image using a known image recognition technology and the area Ac
may be treated as the chest region while the area A1 may be treated
as the lumbar region. Further, any other mode may be used.
[0109] Next, the contrast agent frame identification unit 42
identifies a frame which includes an image signal representing an
image of a contrast agent as the contrast agent frame for each
segmented area segmented by the area setting unit 41 (S30), and the
radiation exposure dose obtaining unit 43 calculates the radiation
exposure dose received by the patient during capturing of each
frame of the fluoroscopic image based on the radiation image
signals of each frame for each segmented area segmented by the area
setting unit 41 (S32).
[0110] More specifically, an E.I. (Exposure Index) is calculated as
a signal evaluation value of each segmented area based on the
radiation image signal of each frame, and the radiation exposure
dose is obtained based on the E.I.
[0111] The E.I. is calculated in the following manner. First, a
predetermined calculation area is set in a radiation image of each
segmented area. The calculation area may be, for example, the
entire area of the radiation image, an area arbitrarily set by the
user, an area defined based on the imaged region information, or an
area within 10% of the image size from the center of the radiation
image. Otherwise, an area except for the so-called direct exposure
area or an area of 90% of the entire density width from the central
density of the radiation image may be employed. Alternatively, a
specific calculation area may be set by combining the
aforementioned conditions.
[0112] Next, a representative value V of the calculation area set
in the above is calculated. As for the representative value V, the
density value itself of the radiation image or a statistical
characteristic value obtained by modifying the density value itself
with the average value of the entire density values, median value,
mode value, or trimmed mean value may be employed. Then, based on
the representative value V, the E.I. of each frame is calculated by
the formula given below:
E.I.=C.sub.0.times.g(V),
where: [0113] g(V): reverse calibration function; and [0114]
C.sub.0: 100Gy (constant)
[0115] The g(V) is a function defined based on a radiation image
obtained with the radiation quality of RQA5. The representative
value V differs in magnitude due to difference in sensitivity
arising from difference in scintillator used in the radiation image
detector or difference in the setting method of the calculation
area or the calculation method of the representative value V and
g(V) is a function to normalize the differences. That is, if RQA5
radiation is received by any type of radiation image detector by
the same radiation dose, the E.I. will become nearly the same
value.
[0116] The radiation exposure dose received by the patient in each
segmented area during imaging of each frame is calculated by the
radiation exposure dose obtaining unit 43 using the E.I. calculated
in the manner described above. As for the method of obtaining the
radiation exposure dose using the E.I., for example, a function
which defines these relationships or a lookup table may be set in
advance.
[0117] Here, in the case where a contrast agent is injected and a
contrast agent image is captured in the middle of the fluoroscopic
image capturing as described above, the radiation applied to the
patient is absorbed by the contrast agent before reaching the
radiation image detector 12, so that if the radiation exposure dose
is calculated based on the radiation image signal of the contrast
agent frame, the calculated dose becomes smaller than that actually
received by the patient.
[0118] The graph on the right in FIG. 4 illustrates the radiation
exposure doses obtained in the manner described above for each
frame in each segmented area connected by a line and the horizontal
axis of the graph indicates the frame number from the start of
imaging. For example, in the case where the amount of radiation
exposure is calculated based on the radiation image signal shown in
the upper most graph on the right in FIG. 4, the radiation exposure
dose in the area where a contrast agent is imaged (depressed area
in the graph) will become smaller than the actual value (estimated
value indicated by the dotted line in the graph).
[0119] Further, as indicated by the dotted line in the drawing on
the left in FIG. 4, the contrast agent injected into the human body
may possibly move with time. In this case, as illustrated in the
graph on the right in FIG. 4, the time or length of the portion
where the radiation exposure dose becomes a smaller value affected
by the contrast agent differs depending on the segmented area, so
that a frame which includes an image signal representing an image
of a contrast agent is identified in the contrast agent frame
identification unit 42 for each segmented area and correction is
performed in the radiation exposure dose obtaining unit 43 to bring
the smaller value closer to the actual value of radiation exposure
dose for the contrast agent frame.
[0120] In the present embodiment, the contrast agent frame
identification is performed such that a frame whose radiation
exposure dose is dipped more than or equal to a predetermined value
with respect to the average of the radiation exposure doses of the
entire graph is identified as a contrast agent frame. For the
correction of the radiation exposure dose, a value corrected by a
linear interpolation using a radiation exposure dose of a frame
other than a contrast agent frame immediately preceding the
contrast agent frame and a radiation exposure dose of a frame other
than a contrast agent frame immediately following the contrast
agent frame is used for each segmented area.
[0121] Then, the radiation exposure dose obtaining unit 43
calculates a radiation exposure dose of the subject for each
segmented area throughout the continuous radiological imaging by
adding radiation exposure doses of all frames of each segmented
area and, based on this, calculates a total radiation exposure dose
for each body region of the patient. More specifically, as the
segmented areas 1 to 6 are categorized as the chest region and the
segmented areas 7 to 9 are categorized as the lumbar region in the
present embodiment, the sum of the radiation exposure doses of
segmented areas 1 to 6 is the total radiation exposure dose of the
chest region while the sum of the radiation exposure doses of
segmented areas 7 to 9 is the total radiation exposure dose of the
lumbar region.
[0122] The total radiation exposure dose of each body region of the
patient obtained in the radiation exposure dose obtaining unit 43
is inputted to the radiation exposure dose management apparatus 50,
and the radiation exposure dose management apparatus 50 registers
the total radiation exposure dose of each body region of the
patient with the ID information of the patient inputted in advance
(S34). Then, the radiation exposure dose management apparatus 50
displays the registered total radiation exposure dose of each body
region of the patient with the ID information of the patient as
required or calculates a cumulative radiation exposure dose from
the past for a particular patient and displays a warning message if
the cumulative radiation exposure dose is greater than a
predetermined specified value.
[0123] When storing the total radiation exposure dose of each body
region of the patient, the use of a standard format may result in
improved convenience. As the standard protocol in the medical image
systems is DICOM (Digital Imaging and COmmunication in Medicine),
storage in a format based on the DICOM is preferable. As for the
saving format of the radiation dose in fluoroscopic image
capturing, the study and proposal have been made by the Working
Group, but the saving format in association with body regions of a
patient is not studied. As such, an example format which takes
account the association of body regions of a patient with the
saving format proposed by the working Group will be described
below.
[0124] FIG. 6 illustrates the current DICOM saving format for
radiation dose of a fluoroscopic image. Note that, in FIG. 6, the
solid line illustrates the contents proposed by the Working Group
while the dotted line illustrates the contents which take account
the saving with body regions of a patient being associated
according to the present embodiment. The saving format of the
radiation dose in fluoroscopic image capturing has a hierarchical
structure and the saving of accumulated dose (detected radiation
dose at the radiation image detector) and the saving of applied
dose (applied radiation dose at the radiation application unit) are
proposed. In FIG. 6, it is assumed that n times of accumulation are
performed, and a format of saving a corresponding accumulated dose
for each time of accumulation is illustrated, but a format in which
the sum of accumulated doses corresponding to each of a plurality
of times of accumulation is saved is also allowed. The same applies
to the applied dose.
[0125] As the radiation exposure dose of the present embodiment
corresponds to the accumulated dose, it is saved under the
hierarchy of "TID (10004) Accumulated Application X-Ray Dose
(accumulated dose)" and a body region of the patient is also
associated therewith and saved. The saving format of body regions
may be a text format, like "abdomen" if the region is abdomen. In
the case where the sum of accumulated doses of a plurality of times
of accumulation for the plurality of times of accumulation is
saved, it is highly likely that the body region of the patient
extends to a plurality of regions and the plurality of body regions
may be saved in a list format with "and", like "chest and abdomen"
if the regions are chest and abdomen.
[0126] In the case where the radiation application unit does not
have any means for measuring the applied dose, no data exists under
the hierarchy of "TID (10003) Irradiation Event X-Ray Data (applied
dose)" and it may cause inconvenience to the subsequent processing.
In such a case, instead of the applied dose, radiation exposure
dose (accumulated dose) may be saved under the hierarchy of "TID
(10003) Irradiation Event X-Ray Data (applied dose)". In this case,
the saving may be performed in the same manner as in the saving
format of the accumulated dose described above.
[0127] According to the radiation image capturing system of the
present embodiment, when obtaining a radiation exposure dose of a
subject during the continuous radiological imaging based on a
radiation image signal of each frame detected by the radiation
image detector through the continuous radiological imaging of the
subject, one or more areas corresponding to a region or regions of
the subject are set in an image represented by the radiation image
signal, and a radiation exposure dose is obtained for each area.
When performing risk management of diseases for patients, this
allows more appropriate management which takes into account
different impacts of radiation on different body regions to be
performed.
[0128] So far, a preferred embodiment of the first radiation
exposure dose obtaining apparatus of the present invention has been
described, but the first radiation exposure dose obtaining
apparatus of the present invention is not limited to the
aforementioned embodiment. For example, a contrast agent frame may
be identified by any method other than the aforementioned method,
such as a method which uses contrast agent frame information to
identify, for example, a frame having contrast agent frame
information appended thereto is identified as a contrast agent
frame or a frame after a predetermined time from the frame having
contrast agent frame information appended thereto is identified as
a contrast agent frame by taking into account the traveling time of
the contrast agent within the body.
[0129] Further, in the radiation image capturing system described
above, a radiation exposure dose of a patient during a contrast
agent frame is captured through linear interpolation of radiation
exposure doses calculated based on radiation image signals of
immediately preceding and immediately following frames of the
contrast agent frame. But the method is not limited to this and any
other method may be used. For example, a radiation exposure dose
calculated based on the radiation image signal of the immediately
preceding or immediately following frame may be employed directly
as the radiation exposure dose during the contrast agent frame
capturing, or a radiation exposure dose calculated based on the
radiation image signal of another frame other than the contrast
agent frame may be employed. Otherwise, a radiation exposure dose
calculated based on the radiation image signal of a contrast agent
frame may be corrected by adding a predetermined radiation exposure
dose determined in advance thereto or by multiplying it with a
given coefficient which is greater than 1.
[0130] Further, the radiation exposure dose obtaining apparatus is
implemented as an independent apparatus in the embodiment described
above, but it may be implemented in any other form, such as being
incorporated in the other apparatus, such as the radiation image
capturing apparatus, as a part thereof. More specifically, it may
be provided in a console which includes the system control
apparatus 60 or in the radiation image capturing apparatus 10.
Further, in the case where the radiation image detector 12 is
accommodated in a portable electronic cassette, and hardware of
electronic circuits, such as LSI (Large Scale Integration),
hardware of programmable electronic circuits, such as PLD
(Programmable Logic Device) FPGA (Field-Programmable Gate Array),
and the like are accommodated in the electronic cassette, the
identification of a contrast agent frame and acquisition of
radiation exposure dose may be performed by the hardware. Such
arrangement allows pursuit of more real time implementation.
[0131] An embodiment of a radiation image capturing system that
uses an embodiment of the second radiation exposure dose obtaining
apparatus of the present invention will now be described with
reference to the accompanying drawings. FIG. 7 is a block diagram
of the radiation image capturing system of the present embodiment,
illustrating an overall schematic configuration thereof.
[0132] As illustrated in FIG. 7, the radiation image capturing
system of the present embodiment includes a radiation image
capturing apparatus 110 which captures fluoroscopic image (moving
picture) of a patient, a radiation image display apparatus 120
which displays the fluoroscopic image captured by the radiation
image capturing apparatus 110, a contrast agent injection apparatus
130 which injects a contrast agent into a blood vessel or a lymph
vessel of the patient, a radiation exposure dose obtaining
apparatus 140 which obtains an exposure dose of the patient based
on an image signal of the fluoroscopic image captured by the
radiation image capturing apparatus 110, a radiation exposure dose
management apparatus 150 which stores and manages the exposure dose
of each patient obtained by the radiation exposure dose obtaining
apparatus 140, a system control apparatus 160 which performs
overall control of the radiation image capturing system.
[0133] As illustrated in FIG. 7, the radiation image capturing
apparatus 110 includes a radiation application unit 111 that has an
X-ray tube, an aperture stop, and the like and applies radiation
emitted from the x-ray tube and passed through the aperture stop to
a patient, a radiation image detector 112 that detects radiation
transmitted through the patient and outputs a radiation image
signal representing a radiation image of the patient, a radiation
image storage unit 113 that stores the radiation image signal
outputted from the radiation image detector 112, and a control unit
114 that performs overall control of the radiation image capturing
apparatus 110.
[0134] The radiation image detector 112 allows repeated use for
recording and reading of radiation images, and a so-called direct
type radiation image detector that records a radiation image by
generating and accumulating a charge by directly receiving
radiation or a so-called indirect type radiation image detector
that records a radiation image by converting radiation first to
visible light and then converting the visible light to a charge and
accumulating the charge may be used. As for the radiation image
signal reading method for reading out the radiation image recorded
by accumulating charges in the manner described above, a so-called
TFT (thin film transistor) reading method in which a radiation
image signal is read by ON/OFF switching thin film transistors and
a so-called optical reading method in which a radiation image
signal is read out by applying reading light are preferably used,
but others may also be used.
[0135] The radiation image capturing apparatus 110 is used to
capture a fluoroscopic image (moving picture) of a subject to be
injected with a contrast agent by the contrast agent injection
apparatus 130, and the control unit 114 controls the radiation
application unit 111 and radiation image detector 112 such that the
fluoroscopic image is captured. More specifically, the control unit
114 controls the radiation application unit 111 to apply radiation
at a predetermined frame rate and the radiation image detector 112
to perform recording and reading of a radiation image by the
application of the radiation. Then, the radiation image signals of
each frame outputted from the radiation image detector 112 are
sequentially stored in the radiation image storage unit 113.
Further, the control unit 114 of the present embodiment appends
information indicating whether or not an image signal representing
an image of the contrast agent is included in the radiation image
signals of each frame when storing the radiation image signal of
each frame in the radiation image storage unit 113, the operation
of which will be described later in detail.
[0136] As for the structure of the radiation image capturing
apparatus 110, a structure in which image capturing is performed
with the patient being in the upright position or in the lateral
position may be employed. Further, a structure that allows image
capturing with the patient being both in upright position and
lateral position may be employed.
[0137] The radiation image display apparatus 120 generates a
display control signal by performing predetermined processing on
the radiation image signals of each frame read out from the
radiation image storage unit 113 of the radiation image capturing
apparatus 110 and displays a fluoroscopic image of the patient on
the monitor based on the display control signal.
[0138] The contrast agent injection apparatus 130 automatically
injects a contrast agent into a patient based on an instruction
input from the user or based on a preset injection start timing of
the contrast agent. More specifically, the contrast agent injection
apparatus 130 includes a contrast agent injection unit 131 formed
of, for example, a syringe and injects a contrast agent into a
blood vessel of the patient or the like, an injection drive unit
132 which drives the injection operation of the contrast agent
injection unit 131, a control unit 133 that controls the operation
of the injection drive unit 132, and a contrast agent injection
detection sensor unit 134 that detects whether or not the contrast
agent is being injected into a blood vessel or the like of the
patient from the contrast agent injection apparatus 130.
[0139] The injection drive unit 132 moves, for example, the piston
of the syringe of the contrast agent injection unit 131 and is
formed of a power means, such as an air pressure, motor, or
hydraulic pressure.
[0140] The contrast agent injection detection sensor unit 134
includes a sensor for detecting that the contrast agent is
discharged from the contrast agent injection unit 131. Then, the
contrast agent injection detection sensor unit 134 outputs a
contrast agent detection signal to the control unit 114 of the
radiation image capturing apparatus 110.
[0141] The radiation exposure dose obtaining apparatus 140 includes
a radiation exposure dose obtaining unit 142 that obtains a
radiation exposure dose of a patient based on a radiation moving
picture signal which is a collection of radiation image signals of
each frame read out from the radiation storage unit 113 of the
radiation image capturing apparatus 110. The operation of the
radiation exposure dose obtaining unit 142 will be described later
in detail.
[0142] The radiation exposure dose management apparatus 150 stores
the radiation exposure dose obtained by the radiation exposure dose
obtaining apparatus 140 and manages the radiation exposure dose of
each patient.
[0143] The system control apparatus 160 outputs control signals to
the radiation image capturing apparatus 110, the radiation image
display apparatus 120, the contrast agent injection apparatus 130,
the radiation exposure dose obtaining apparatus 140, and the
radiation exposure dose management apparatus 150 to control the
operations thereof and at the same time performs input/output
signal control between these apparatuses. The system control
apparatus 160 is provided with an input unit 170 which receives an
instruction input and other inputs, such as image capturing
conditions, patient ID information and the like, from the user. The
input information received by the input unit 170 is outputted to
each apparatus by the system control apparatus 160 as required.
[0144] An operation of the radiation image capturing system of the
present embodiment will now be described with reference to the
flowchart of FIG. 8.
[0145] First, a patient, the subject of the image capturing, is
placed on an image capturing platform or the like provided in the
radiation image capturing apparatus 110 and the patient is put into
position (S110).
[0146] Then, ID information of the image capturing target patient
and an image capturing condition are inputted by the user through
the input unit 170 and the patient ID information is registered in
the radiation exposure dose management apparatus 150 while the
image capturing condition is set to the control unit 114 of the
radiation image capturing apparatus 110 (S112). The image capturing
condition may include a tube voltage, tube current, and application
time in order to apply an appropriate dose of radiation to an image
capturing region of the patient, as well as a frame rate for
capturing a fluoroscopic image. As for the frame rate for capturing
the fluoroscopic image, for example, a frame rate of 5 fps to 60
fps is set.
[0147] Next, an instruction to start fluoroscopic image capturing
of the patient is inputted by the user through the input unit 170
and in response to the input, a control signal is outputted from
the system control apparatus 160 to the radiation image capturing
apparatus 110 to capture a fluoroscopic image, and the radiation
image capturing apparatus 110 starts fluoroscopic image capturing
according to the inputted control signal (S114).
[0148] More specifically, the X-ray tube of the radiation
application unit 111 is controlled based on the inputted imaging
condition and a predetermined dose of radiation is applied toward
the patient intermittently at a predetermined frame rate.
[0149] Then, radiation transmitted through the patient is applied
to the radiation image detector 112 and subjected to a
photoelectrical conversion in the radiation image detector 112 and
accumulated therein as a charge signal.
[0150] Thereafter, each time the application of radiation for each
frame is ended, the charge signal accumulated in the radiation
image detector 112 is read out by the control unit 114, then
converted to a digital signal by an A/D converter (not shown), and
stored in the radiation image storage unit 113.
[0151] FIG. 9 is a timing chart illustrating the application timing
of radiation from the X-ray tube of the radiation application unit
111 and the charge accumulation timing of the radiation image
detector 112. The period during which no charge accumulation is
performed in the radiation image detector 112 (accumulation OFF
period) is a period for reading out a charge signal from the
radiation image detector 112.
[0152] The repeated performance of radiation application by the
X-ray tube and the radiation image recording and reading in the
radiation image detector 112 at a predetermined frame rate in the
manner described above causes the radiation image signal of each
frame to be sequentially stored in the radiation image storage unit
113.
[0153] Then, the radiation image signals of each frame stored in
the radiation image storage apparatus 113 are sequentially read out
and outputted to the radiation image display apparatus 120. The
radiation image display apparatus 120 sequentially generates
display control signals based on the inputted radiation image
signals of each frame and sequentially outputs the display control
signals to the monitor to display a fluoroscopic image of the
patient as a moving picture (S116). It is assumed here that the
radiation image signals with respect each frame stored in the
radiation image storage unit 113 will remain un-erased in the
radiation image storage unit 113 after being read out.
[0154] Here, if the user desires to observe a contrast agent image,
such as a blood vessel or the like, while the fluoroscopic image
capturing and display are performed in the manner described above,
a contrast agent injection instruction is inputted through the
input unit 170 (S118).
[0155] When the contrast agent injection instruction is inputted
through the input unit 170, a control signal is outputted from the
system control apparatus 160 to the contrast agent injection
apparatus 130. The contrast agent injection apparatus 130 starts
contrast agent injection based on the inputted control signal. More
specifically, the contrast agent injection unit 131 is driven by
the injection drive unit 132 and a predetermined amount of contrast
agent is discharged from the contrast agent injection unit 131.
[0156] Here, the contrast agent injection detection sensor unit 134
provided in the contrast agent injection apparatus 130 detects that
the contrast agent is discharged and a detection signal is
outputted to the control unit 114 of the radiation image capturing
apparatus 110 (S120). When the contrast agent detection signal is
inputted, the control unit 114 of the radiation image capturing
apparatus 110 appends to the radiation image signal of a frame
captured while the contrast agent detection signal is inputted
information indicating that it includes an image signal
representing an image of the contrast agent (hereinafter, referred
to as "contrast agent frame information") as header information,
and stores the radiation image signal in the radiation image
storage unit 113 with the header information (S122). More
specifically, if the contrast agent detection signal is inputted to
the radiation image capturing apparatus 110 in the timing
illustrated in FIG. 9, the contrast agent frame information is
appended to the radiation image signals of frames F1 and F2
captured while the contrast agent is injected and stored in the
radiation image storage unit 113.
[0157] Then, the radiation image signals captured while the
contrast agent is injected are also read out from the radiation
image storage unit 113 and sequentially outputted to the radiation
image display apparatus 120. The radiation image display apparatus
120 sequentially generates display control signals based on the
inputted radiation image signals, and displays radiation images
including a contrast agent image on the monitor based on the
display control signals (S124).
[0158] Then, after the discharge of the predetermined amount of
contrast agent from the contrast agent injection apparatus 130 is
completed and the contrast agent detection signal is not detected
any more in the contrast agent injection detection sensor unit 134,
radiation image signals captured are stored in the radiation image
storage unit 113 without the contrast agent frame information being
appended, and radiation image signals with respect each frame are
read out from the radiation image storage unit 113 in the manner
described above and a fluoroscopic image is displayed on the
radiation image display apparatus 120.
[0159] Thereafter, when an instruction to end the fluoroscopic
image capturing is inputted by the user through the input unit 170,
the system control apparatus 160 outputs a control signal to the
radiation image capturing apparatus 110 to end the fluoroscopic
image capturing, and the radiation image capturing apparatus 110
ends the fluoroscopic image capturing in response to the inputted
control signal (S126).
[0160] When the fluoroscopic image capturing described above is
ended, the system control apparatus 160 reads out radiation image
signals of all frames, i.e., the radiation moving picture signal,
stored in the radiation image storage unit 113 of the radiation
image capturing apparatus 110 and inputs the radiation image
signals to the radiation exposure dose obtaining apparatus 140.
[0161] Then, a radiation image signal of a frame to which contrast
agent frame information is appended is identified first, as
required, from the radiation moving picture signal and the frame is
identified as a contrast agent frame (S128).
[0162] Next, the radiation exposure dose obtaining unit 142
calculates the radiation exposure dose received by the patient
during capturing of the fluoroscopic image based on radiation image
signals of each frame (S130).
[0163] More specifically, an E.I. (Exposure Index) is calculated as
a signal evaluation value Rf based on a radiation image signal of
the first frame of the radiation moving picture signal.
[0164] The E.I. is calculated in the following manner. First, a
predetermined calculation area is set in a radiation image of each
frame. The calculation area may be, for example, the entire area of
the radiation image, an area arbitrarily set by the user, an area
defined based on the imaged region information, or an area within
10% of the image size from the center of the radiation image.
Otherwise, an area except for the so-called direct exposure area
which may be obtained based on, for example, a histogram of the
radiation image or an area of 90% of the entire density width from
the central density of the radiation image may be employed.
Alternatively, a specific calculation area may be set by combining
the aforementioned conditions.
[0165] Next, a representative value V of the calculation area set
in the above is calculated. As for the representative value V, the
density value itself of the radiation image or a statistical
characteristic value obtained by modifying the density value itself
with the average value of the entire density values, median value,
mode value, or trimmed mean value may be employed. Then, based on
the representative value V, the E.I. of each frame is calculated by
the formula given below:
E.I.=C.sub.0.times.g(V),
where: [0166] g(V): reverse calibration function; and [0167]
C.sub.0: 100Gy (constant).
[0168] Here, g(V) is a function defined based on a radiation image
obtained with the radiation quality of RQA5. The representative
value V differs in magnitude due to difference in sensitivity
arising from difference in scintillator used in the radiation image
detector or difference in the setting method of the calculation
area or the calculation method of the representative value V and
g(V) is a function to normalize the differences. That is, if RQA5
radiation is received by any type of radiation image detector by
the same radiation dose, the E.I. will become nearly the same
value.
[0169] Next, an E.I. of the radiation moving picture signal
(collection of radiation image signals of each frame) is calculated
by the formula (1) and a radiation exposure dose of the subject
during the continuous radiological imaging based on the calculated
E.I. of the radiation moving picture signal. As for the method of
obtaining the radiation exposure dose using the E.I., for example,
a function which defines these relationships or a lookup table may
be set in advance.
Rm=Rf.times.N (1)
where:
[0170] Rm: E.I. of the entire radiation moving picture signal
(signal evaluation value of the entire radiation moving picture
signal);
[0171] N: number of frames of the entire radiation moving picture
signal; and
[0172] Rf: E.I. of the radiation image signal of the first frame of
the radiation moving picture signal.
[0173] In the case where a contrast agent is injected and a
contrast agent image is captured in the middle of the fluoroscopic
image capturing as described above, the radiation applied to the
patient is absorbed by the contrast agent before reaching the
radiation image detector 112, as illustrated in the graph shown at
the bottom of FIG. 9. Therefore, if a radiation exposure dose is
calculated for each frame based simply on a radiation image signal
of each frame and a radiation exposure dose of the entire moving
picture (radiation exposure dose of the subject due to the
continuous radiological imaging) is obtained by adding radiation
exposure doses of all the frames of the moving picture, the
obtained radiation exposure dose becomes smaller than that actually
received by the patient.
[0174] The graph at the bottom of FIG. 9 illustrates the radiation
exposure dose of each frame connected by a line and the horizontal
axis of the graph indicates the frame number from the start of
imaging. More specifically, if a radiation exposure dose is
calculated based on the radiation image signals of frames F1, F2
which are deemed to have a contrast agent image illustrated in FIG.
9, the calculated radiation exposure dose will become smaller than
the actual value (estimated value indicated by the dash-dot line in
the graph of FIG. 9).
[0175] Further, even in a frame deemed not to have a contrast agent
image following the frames F1, F2, the signal value of the entire
image is slightly varied due to a residual contrast agent in the
subject and the radiation exposure dose becomes smaller than the
actual value (estimated value indicated by the dash-dot line in the
graph of FIG. 9), though not so great as those of the frames F1, F2
deemed to have a contrast agent image due to the same reason as in
the frames F1, F2. Note that shape of the graph is illustrated in
an exaggerated manner than the actual variation in order to clearly
indicate the nature of the variation.
[0176] In the present embodiment, however, the E.I. of the entire
radiation moving picture signal is calculated by the formula (1)
capable of performing the calculation without using information of
a frame which includes a source of error and a radiation exposure
dose of the subject throughout the continuous radiological imaging
is obtained based on the calculated E.I. of the entire radiation
moving picture signal as described above, so that an accurate
radiation exposure dose of the subject may be obtained. Further,
this requires only a simple calculation and the processing load may
be reduced.
[0177] The total radiation exposure dose obtained in the radiation
exposure dose obtaining unit 142 in the manner described above is
inputted to the radiation exposure dose management apparatus 150,
and the radiation exposure dose management apparatus 150 registers
the total radiation exposure dose with the ID information of the
patient inputted in advance (S132). Then, the radiation exposure
dose management apparatus 150 displays the registered total
radiation exposure dose with the ID information of the patient as
required or calculates a cumulative radiation exposure dose from
the past for a particular patient and displays a warning message if
the cumulative radiation exposure dose is greater than a
predetermined specified value.
[0178] So far, a preferred embodiment of the second radiation
exposure dose obtaining apparatus of the present invention has been
described, but the second radiation exposure dose obtaining
apparatus of the present invention is not limited to the
aforementioned embodiment. For example, the signal evaluation value
Rf of a radiation image signal of predetermined one frame required
for the calculation by the formula (1) is not limited to the signal
evaluation value of the radiation image signal of the first frame
of the radiation moving picture signal described in the
aforementioned embodiment. The signal evaluation value may be
obtained by equipping the radiation image capturing apparatus 10
with a dose measurement switch (not shown), then when storing a
radiation image signal of a frame immediately after the dose
measurement switch is depressed during the continuous radiological
imaging in the radiation image storage unit 113, appending
information which indicates that this frame is the reference frame
at the time of calculating the radiation exposure dose in the
radiation image signal of the frame, and employing a signal
evaluation value calculated based on the radiation image signal of
the frame to which the information is appended as the signal
evaluation value. Further, any other form may be employed as long
as it is a signal evaluation value of a radiation image signal for
one frame deemed to be free of error factor, such as a maximum
signal evaluation value of those calculated for each radiation
image signal, a signal evaluation value of one particular frame
which does not include any error factor such as the contrast agent
described above, an average value of signal evaluation values of
radiation image signals of a plurality of frames that do not
include any error factor, or the like.
[0179] Further, the radiation exposure dose obtaining apparatus is
implemented as an independent apparatus in the embodiment described
above, but it may be implemented in any other form, such as being
incorporated in the other apparatus, such as the radiation image
capturing apparatus, as a part thereof. More specifically, it may
be provided in a console which includes the system control
apparatus 160 or in the radiation image capturing apparatus 110.
Further, in the case where the radiation image detector 112 is
accommodated in a portable electronic cassette, and hardware of
electronic circuits, such as LSI (Large Scale Integration),
hardware of programmable electronic circuits, such as PLD
(Programmable Logic Device) .cndot. FPGA (Field-Programmable Gate
Array), and the like are accommodated in the electronic cassette,
the identification of a contrast agent frame and acquisition of
radiation exposure dose may be performed by the hardware. Such
arrangement allows pursuit of more real time implementation.
[0180] An embodiment of a radiation image capturing system that
uses an embodiment of the third radiation exposure dose obtaining
apparatus of the present invention will now be described with
reference to the accompanying drawings. FIG. 10 is a block diagram
of the radiation image capturing system of the present embodiment,
illustrating an overall schematic configuration thereof.
[0181] As illustrated in FIG. 10, the radiation image capturing
system of the present embodiment includes a radiation image
capturing apparatus 210 which captures a fluoroscopic image (moving
picture) of a patient, a radiation image display apparatus 220
which displays the fluoroscopic image captured by the radiation
image capturing apparatus 210, a contrast agent injection apparatus
230 which injects a contrast agent into a blood vessel or a lymph
vessel of the patient, a radiation exposure dose obtaining
apparatus 240 which obtains an exposure dose of the patient based
on an image signal of the fluoroscopic image captured by the
radiation image capturing apparatus 210, a radiation exposure dose
management apparatus 250 which stores and manages the exposure dose
of each patient obtained by the radiation exposure dose obtaining
apparatus 240, and a system control apparatus 260 which performs
overall control of the radiation image capturing system.
[0182] As illustrated in FIG. 10, the radiation image capturing
apparatus 210 includes a radiation application unit 211 that has an
X-ray tube, an aperture stop, and the like and applies radiation
emitted from the x-ray tube and passed through the aperture stop to
a patient, a radiation image detector 212 that detects radiation
transmitted through the patient and outputs a radiation image
signal representing a radiation image of the patient, a radiation
image storage unit 213 that stores the radiation image signal
outputted from the radiation image detector 212, and a control unit
214 that performs overall control of the radiation image capturing
apparatus 210.
[0183] The radiation image detector 212 allows repeated use for
recording and reading of radiation images, and a so-called direct
type radiation image detector that records a radiation image by
generating and accumulating a charge by directly receiving
radiation or a so-called indirect type radiation image detector
that records a radiation image by converting radiation first to
visible light and then converting the visible light to a charge and
accumulating the charge may be used. As for the radiation image
signal reading method for reading out the radiation image recorded
by accumulating charges in the manner described above, a so-called
TFT (thin film transistor) reading method in which a radiation
image signal is read by ON/OFF switching thin film transistors and
a so-called optical reading method in which a radiation image
signal is read out by applying reading light are preferably used,
but others may also be used.
[0184] The radiation image capturing apparatus 210 is used to
capture a fluoroscopic image (moving picture) of a subject to be
injected with a contrast agent by the contrast agent injection
apparatus 230, and the control unit 214 controls the radiation
application unit 211 and radiation image detector 212 such that the
fluoroscopic image is captured. More specifically, the control unit
214 controls the radiation application unit 211 to apply radiation
at a predetermined frame rate and the radiation image detector 212
to perform recording and reading of a radiation image by the
application of the radiation. Then, the radiation image signals of
each frame outputted from the radiation image detector 212 are
sequentially stored in the radiation image storage unit 213.
Further, the control unit 214 of the present embodiment appends
information indicating whether or not an image signal representing
an image of the contrast agent is included in the radiation image
signals of each frame when storing the radiation image signals of
each frame in the radiation image storage unit 213, the operation
of which will be described later in detail.
[0185] As for the structure of the radiation image capturing
apparatus 210, a structure in which image capturing is performed
with the patient being in the upright position or in the lateral
position may be employed. Further, a structure that allows image
capturing with the patient being both in upright position and
lateral position may be employed.
[0186] The radiation image display apparatus 220 generates a
display control signal by performing predetermined processing on
the radiation image signals of each frame read out from the
radiation image storage unit 213 of the radiation image capturing
apparatus 210 and displays a fluoroscopic image of the patient on
the monitor based on the display control signal.
[0187] The contrast agent injection apparatus 230 automatically
injects a contrast agent into a patient based on an instruction
input from the user or based on a preset injection start timing of
the contrast agent. More specifically, the contrast agent injection
apparatus 230 includes a contrast agent injection unit 231 formed
of, for example, a syringe and injects a contrast agent into a
blood vessel of the patient or the like, an injection drive unit
232 which drives the injection operation of the contrast agent
injection unit 31, a control unit 233 that controls the operation
of the injection drive unit 232, and a contrast agent injection
detection sensor unit 234 that detects whether or not the contrast
agent is being injected into a blood vessel or the like of the
patient from the contrast agent injection apparatus 230.
[0188] The injection drive unit 232 moves, for example, the piston
of the syringe of the contrast agent injection unit 231 and is
formed of a power means, such as an air pressure, motor, or
hydraulic pressure.
[0189] The contrast agent injection detection sensor unit 234
includes a sensor for detecting that the contrast agent is
discharged from the contrast agent injection unit 231. Then, the
contrast agent injection detection sensor unit 234 outputs a
contrast agent detection signal to the control unit 214 of the
radiation image capturing apparatus 210.
[0190] The radiation exposure dose obtaining apparatus 240 includes
a contrast agent frame identification unit 241 that identifies a
radiation image signal of a frame which includes an image signal of
an image of a contrast agent as a contrast agent frame from the
radiation image signal of each frame read out from the radiation
image storage unit 213 of the radiation image capturing apparatus
210, and a radiation exposure dose obtaining unit 242 that obtains
a radiation exposure dose of the patient based on a radiation
moving picture signal which is the collection of the radiation
image signals of each frame read out from the radiation image
storage unit 213 of the radiation image capturing apparatus 210.
Operations of the contrast agent frame identification unit 241 and
the radiation exposure dose obtaining unit 242 will be described
later in detail.
[0191] The radiation exposure dose management apparatus 250 stores
the radiation exposure dose obtained by the radiation exposure dose
obtaining apparatus 240 and manages the radiation exposure dose of
each patient.
[0192] The system control apparatus 260 outputs control signals to
the radiation image capturing apparatus 210, the radiation image
display apparatus 220, the contrast agent injection apparatus 230,
the radiation exposure dose obtaining apparatus 240, and the
radiation exposure dose management apparatus 250 to control the
operations thereof and at the same time performs input/output
signal control between these apparatuses. The system control
apparatus 260 is provided with an input unit 270 which receives an
instruction input and other inputs, such as image capturing
conditions, patient ID information and the like, from the user. The
input information received by the input unit 270 is outputted to
each apparatus by the system control apparatus 260 as required.
[0193] An operation of the radiation image capturing system of the
present embodiment will now be described with reference to the
flowchart of FIG. 11.
[0194] First, a patient, the subject of the image capturing, is
placed on an image capturing platform or the like provided in the
radiation image capturing apparatus 210 and the patient is put into
position (S210).
[0195] Then, ID information of the image capturing target patient
and an image capturing condition are inputted by the user through
the input unit 270 and the patient ID information is registered in
the radiation exposure dose management apparatus 250 while the
image capturing condition is set to the control unit 214 of the
radiation image capturing apparatus 210 (S212). The image capturing
condition may include a tube voltage, tube current, and application
time in order to apply an appropriate dose of radiation to an image
capturing region of the patient, as well as a frame rate for
capturing a fluoroscopic image. As for the frame rate for capturing
the fluoroscopic image, for example, a frame rate of 5 fps to 60
fps is set.
[0196] Next, an instruction to start fluoroscopic image capturing
of the patient is inputted by the user through the input unit 270
and in response to the input, a control signal is outputted from
the system control apparatus 260 to the radiation image capturing
apparatus 210 to capture a fluoroscopic image, and the radiation
image capturing apparatus 210 starts fluoroscopic image capturing
according to the inputted control signal (S214).
[0197] More specifically, the X-ray tube of the radiation
application unit 211 is controlled based on the inputted imaging
condition and a predetermined dose of radiation is applied toward
the patient intermittently at a predetermined frame rate.
[0198] Then, radiation transmitted through the patient is applied
to the radiation image detector 212 and subjected to a
photoelectrical conversion in the radiation image detector 212 and
accumulated therein as a charge signal.
[0199] Thereafter, each time the application of radiation for each
frame is ended, the charge signal accumulated in the radiation
image detector 212 is read out by the control unit 214, then
converted to a digital signal by an A/D converter (not shown), and
stored in the radiation image storage unit 213.
[0200] FIG. 12 is a timing chart illustrating the application
timing of radiation from the X-ray tube of the radiation
application unit 211 and the charge accumulation timing of the
radiation image detector 212. The period during which no charge
accumulation is performed in the radiation image detector 212
(accumulation OFF period) is a period for reading out a charge
signal from the radiation image detector 212.
[0201] The repeated performance of radiation application by the
X-ray tube and the radiation image recording and reading in the
radiation image detector 212 at a predetermined frame rate in the
manner described above causes the radiation image signal of each
frame to be sequentially stored in the radiation image storage unit
213.
[0202] Then, the radiation image signals of each frame stored in
the radiation image storage apparatus 213 are sequentially read out
and outputted to the radiation image display apparatus 220. The
radiation image display apparatus 220 sequentially generates
display control signals based on the inputted radiation image
signals of each frame and sequentially outputs the display control
signals to the monitor to display a fluoroscopic image of the
patient as a moving picture (S216). It is assumed here that the
radiation image signals with respect each frame stored in the
radiation image storage unit 213 will remain un-erased in the
radiation image storage unit 213 after being read out.
[0203] Here, if the user desires to observe a contrast agent image,
such as a blood vessel or the like, while the fluoroscopic image
capturing and display are performed in the manner described above,
a contrast agent injection instruction is inputted through the
input unit 270 (S218).
[0204] When the contrast agent injection instruction is inputted
through the input unit 270, a control signal is outputted from the
system control apparatus 260 to the contrast agent injection
apparatus 230. The contrast agent injection apparatus 230 starts
contrast agent injection based on the inputted control signal. More
specifically, the contrast agent injection unit 231 is driven by
the injection drive unit 232 and a predetermined amount of contrast
agent is discharged from the contrast agent injection unit 231.
[0205] Here, the contrast agent injection detection sensor unit 234
provided in the contrast agent injection apparatus 230 detects that
the contrast agent is discharged and a detection signal is
outputted to the control unit 214 of the radiation image capturing
apparatus 210 (S220). When the contrast agent detection signal is
inputted, the control unit 214 of the radiation image capturing
apparatus 210 appends to the radiation image signal of a frame
captured while the contrast agent detection signal is inputted
information indicating that it includes an image signal
representing an image of the contrast agent (hereinafter, referred
to as "contrast agent frame information") as header information,
and stores the radiation image signal in the radiation image
storage unit 213 with the header information (S222). More
specifically, if the contrast agent detection signal is inputted to
the radiation image capturing apparatus 210 in the timing
illustrated in FIG. 12, the contrast agent frame information is
appended to the radiation image signals of frames F1 and F2
captured while the contrast agent is injected and stored in the
radiation image storage unit 213.
[0206] Then, the radiation image signals captured while the
contrast agent is injected are also read out from the radiation
image storage unit 213 and sequentially outputted to the radiation
image display apparatus 220. The radiation image display apparatus
220 sequentially generates display control signals based on the
inputted radiation image signals, and displays radiation images
including a contrast agent image on the monitor based on the
display control signals (S224).
[0207] Then, after the discharge of the predetermined amount of
contrast agent from the contrast agent injection apparatus 230 is
completed and the contrast agent detection signal is not detected
any more in the contrast agent injection detection sensor unit 234,
radiation image signals captured are stored in the radiation image
storage unit 213 without the contrast agent frame information being
appended, and radiation image signals with respect each frame are
read out from the radiation image storage unit 213 in the manner
described above and a fluoroscopic image is displayed on the
radiation image display apparatus 220.
[0208] Thereafter, when an instruction to end the fluoroscopic
image capturing is inputted by the user through the input unit 270,
the system control apparatus 260 outputs a control signal to the
radiation image capturing apparatus 210 to end the fluoroscopic
image capturing, and the radiation image capturing apparatus 210
ends the fluoroscopic image capturing in response to the inputted
control signal (S226).
[0209] When the fluoroscopic image capturing described above is
ended, the system control apparatus 260 reads out radiation image
signals of all frames, i.e., the radiation moving picture signal,
stored in the radiation image storage unit 213 of the radiation
image capturing apparatus 210, and inputs the radiation image
signals to the radiation exposure dose obtaining apparatus 240.
[0210] Then, first, the contrast agent frame identification unit
241 identifies a radiation image signal of a frame to which
contrast agent frame information is appended from the radiation
moving picture signal and identifies the frame as a contrast agent
frame (S228).
[0211] Next, the radiation exposure dose obtaining unit 242
calculates a radiation exposure dose received by the patient during
capturing of the fluoroscopic image based on the radiation image
signals of each frame (S230).
[0212] More specifically, an E.I. (Exposure Index) is calculated as
a signal evaluation value for each frame based on a radiation image
signal of each frame other than a contrast agent frame.
[0213] The E.I. is calculated in the following manner. First, a
predetermined calculation area is set in a radiation image of each
frame. The calculation area may be, for example, the entire area of
the radiation image, an area arbitrarily set by the user, an area
defined based on the imaged region information, or an area within
10% of the image size from the center of the radiation image.
Otherwise, an area except for the so-called direct exposure area
which may be obtained based on, for example, a histogram of the
radiation image or an area of 90% of the entire density width from
the central density of the radiation image may be employed.
Alternatively, a specific calculation area may be set by combining
the aforementioned conditions.
[0214] Next, a representative value V of the calculation area set
in the above is calculated. As for the representative value V, the
density value itself of the radiation image or a statistical
characteristic value obtained by modifying the density value itself
with the average value of the entire density values, median value,
mode value, or trimmed mean value may be employed. Then, based on
the representative value V, the E.I. of each frame is calculated by
the formula given below:
E.I.=C.sub.0.times.g(V),
where: [0215] g(V): reverse calibration function; and [0216]
C.sub.0: 1001]Gy (constant).
[0217] Here, g(V) is a function defined based on a radiation image
obtained with the radiation quality of RQA5. The representative
value V differs in magnitude due to difference in sensitivity
arising from difference in scintillator used in the radiation image
detector or difference in the setting method of the calculation
area or the calculation method of the representative value V and
g(V) is a function to normalize the differences. That is, if RQA5
radiation is received by any type of radiation image detector by
the same radiation dose, the E.I. will become nearly the same
value.
[0218] As described above, an E.I. is calculated first for each
frame, then an E.I. of the radiation moving picture signal
(collection of radiation image signals of each frame) is
calculated, and a radiation exposure dose of the subject due to the
continuous radiological imaging is obtained based on the calculated
E.I. of the radiation moving picture signal. In the case where a
contrast agent is injected and a contrast agent image is captured
in the middle of the fluoroscopic image capturing as described
above, the radiation applied to the patient is absorbed by the
contrast agent before reaching the radiation image detector 212, as
illustrated in the graph shown at the bottom of FIG. 12. Therefore,
if a radiation exposure dose is calculated based on a radiation
image signal of a contrast agent frame, the calculated value
becomes smaller than that actually received by the patient.
[0219] The graph at the bottom of FIG. 12 illustrates the radiation
exposure dose of each frame connected by a line and the horizontal
axis of the graph indicates the frame number from the start of
imaging. More specifically, if a radiation exposure dose is
calculated based on the radiation image signals of frames F1, F2
illustrated in FIG. 12, the calculated radiation exposure dose will
become smaller than the actual value (estimated value close to the
line connecting the frames immediately preceding and following the
frames F1, F2 which includes a contrast agent image).
[0220] Consequently, in the present embodiment, an E.I. of the
radiation moving picture signal (collection of radiation image
signals of each frame) is calculated by the formula (11) and a
radiation exposure dose of the subject is obtained based on the
calculated E.I. of the radiation moving picture signal. Note that
the same value can be obtained by the formula (13).
Rm=Rs.times.N/(N-M) (11)
Rm=Ra.times.N (13),
where:
[0221] Rm: E.I. of the entire radiation moving picture signal
(signal evaluation value of the entire radiation moving picture
signal);
[0222] N: number of frames of the entire radiation moving picture
signal;
[0223] M: number of contrast agent frames in the radiation moving
picture signal;
[0224] Rs: sum of E. I. of the radiation image signals of each
frame other than a contrast agent frame; and
[0225] Ra: average value of E. I. of the radiation image signals of
each frame other than a contrast agent frame.
[0226] The formulae (11), (13) calculate an E.I. of the entire
radiation moving picture signal without using an E.I. of a contrast
agent frame and interpolating the E.I. for the contrast agent frame
using E.I. of the frames other than the contrast agent frame.
[0227] Then, a radiation exposure dose of the subject due to the
continuous radiological imaging is obtained using the E.I. of the
entire radiation moving picture signal calculated in the manner
described above. As for the method of obtaining the radiation
exposure dose using the E.I., for example, a function which defines
these relationships or a lookup table may be set in advance.
[0228] The total radiation exposure dose obtained in the radiation
exposure dose obtaining unit 242 is inputted to the radiation
exposure dose management apparatus 250, and the radiation exposure
dose management apparatus 250 registers the total radiation
exposure dose for each body region of the patient with the ID
information of the patient inputted in advance (S232). Then, the
radiation exposure dose management apparatus 250 displays the
registered total radiation exposure dose with the ID information of
the patient as required or calculates a cumulative radiation
exposure dose from the past for a particular patient and displays a
warning message if the cumulative radiation exposure dose is
greater than a predetermined specified value.
[0229] According to the radiation image capturing system of the
present embodiment, a frame which includes an image signal
representing an image of a contrast agent is identified as a
contrast agent frame from the radiation image signal of each frame,
then a signal evaluation value of the radiation moving picture is
calculated by the formula (11) or (13) which does not use
information of the contrast agent frame, and a radiation exposure
dose of the subject throughout the continuous radiological imaging
is obtained based on the calculated signal evaluation value of the
radiation moving picture signal. This allows more accurate
radiation exposure dose of a subject which takes into account the
inclusion of an image of a contrast agent in the radiation image to
be obtained.
[0230] So far, a preferred embodiment of the third radiation
exposure dose obtaining apparatus of the present invention has been
described, but the third radiation exposure dose obtaining
apparatus of the present invention is not limited to the
aforementioned embodiment.
[0231] For example, a contrast agent frame may be identified by any
method other than the aforementioned method that uses the contrast
agent injection detection sensor described above, such as a method
in which a contrast agent injection time obtaining unit is provided
and injection start and end time of the contrast agent are obtained
by the contrast agent injection time obtaining unit and a contrast
agent frame is obtained based on the time information, a method
which identifies a frame whose signal evaluation value is within a
predetermined range and differs from that of a frame other than the
contrast agent from as a contrast agent frame without using these
sensors, or the like.
[0232] Further, the radiation exposure dose obtaining apparatus is
implemented as an independent apparatus in the embodiment described
above, but it may be implemented in any other form, such as being
incorporated in the other apparatus, such as the radiation image
capturing apparatus, as a part thereof. More specifically, it may
be provided in a console which includes the system control
apparatus 260 or in the radiation image capturing apparatus 210.
Further, in the case where the radiation image detector 212 is
accommodated in a portable electronic cassette, and hardware of
electronic circuits, such as LSI (Large Scale Integration),
hardware of programmable electronic circuits, such as PLD
(Programmable Logic Device) .cndot. FPGA (Field-Programmable Gate
Array), and the like are accommodated in the electronic cassette,
the identification of a contrast agent frame and acquisition of
radiation exposure dose may be performed by the hardware. Such
arrangement allows pursuit of more real time implementation.
[0233] An embodiment of a radiation image capturing system that
uses an embodiment of the fourth radiation exposure dose obtaining
apparatus of the present invention will now be described with
reference to the accompanying drawings. FIG. 13 is a block diagram
of the radiation image capturing system of the present embodiment,
illustrating an overall schematic configuration thereof.
[0234] As illustrated in FIG. 13, the radiation image capturing
system of the present embodiment includes a radiation image
capturing apparatus 310 which captures a fluoroscopic image (moving
picture) of a patient, a radiation image display apparatus 320
which displays the fluoroscopic image captured by the radiation
image capturing apparatus 210, a contrast agent injection apparatus
330 which injects a contrast agent into a blood vessel or a lymph
vessel of the patient, a radiation exposure dose obtaining
apparatus 340 which obtains an exposure dose of the patient based
on an image signal of the fluoroscopic image captured by the
radiation image capturing apparatus 310, a radiation exposure dose
management apparatus 350 which stores and manages the exposure dose
of each patient obtained by the radiation exposure dose obtaining
apparatus 340, and a system control apparatus 360 which performs
overall control of the radiation image capturing system.
[0235] As illustrated in FIG. 10, the radiation image capturing
apparatus 310 includes a radiation application unit 311 that has an
X-ray tube, an aperture stop, and the like and applies radiation
emitted from the x-ray tube and passed through the aperture stop to
a patient, a radiation image detector 312 that detects radiation
transmitted through the patient and outputs a radiation image
signal representing a radiation image of the patient, a radiation
image storage unit 313 that stores the radiation image signal
outputted from the radiation image detector 312, and a control unit
314 that performs overall control of the radiation image capturing
apparatus 310.
[0236] The radiation image detector 312 allows repeated use for
recording and reading of radiation images, and a so-called direct
type radiation image detector that records a radiation image by
generating and accumulating a charge by directly receiving
radiation or a so-called indirect type radiation image detector
that records a radiation image by converting radiation first to
visible light and then converting the visible light to a charge and
accumulating the charge may be used. As for the radiation image
signal reading method for reading out the radiation image recorded
by accumulating charges in the manner described above, a so-called
TFT (thin film transistor) reading method in which a radiation
image signal is read by ON/OFF switching thin film transistors and
a so-called optical reading method in which a radiation image
signal is read out by applying reading light are preferably used,
but others may also be used.
[0237] The radiation image capturing apparatus 310 is used to
capture a fluoroscopic image (moving picture) of a subject to be
injected with a contrast agent by the contrast agent injection
apparatus 330, and the control unit 314 controls the radiation
application unit 311 and radiation image detector 312 such that the
fluoroscopic image is captured. More specifically, the control unit
314 controls the radiation application unit 311 to apply radiation
at a predetermined frame rate and the radiation image detector 312
to perform recording and reading of a radiation image by the
application of the radiation. Then, the radiation image signals of
each frame outputted from the radiation image detector 312 are
sequentially stored in the radiation image storage unit 313.
Further, the control unit 314 of the present embodiment appends
information indicating whether or not an image signal representing
an image of the contrast agent is included in the radiation image
signals of each frame when storing the radiation image signals of
each frame in the radiation image storage unit 313, the operation
of which will be described later in detail.
[0238] As for the structure of the radiation image capturing
apparatus 310, a structure in which image capturing is performed
with the patient being in the upright position or in the lateral
position may be employed. Further, a structure that allows image
capturing with the patient being both in upright position and
lateral position may be employed.
[0239] The radiation image display apparatus 320 generates a
display control signal by performing predetermined processing on
the radiation image signals of each frame read out from the
radiation image storage unit 313 of the radiation image capturing
apparatus 310 and displays a fluoroscopic image of the patient on
the monitor based on the display control signal.
[0240] The contrast agent injection apparatus 330 automatically
injects a contrast agent into a patient based on an instruction
input from the user or based on a preset injection start timing of
the contrast agent. More specifically, the contrast agent injection
apparatus 330 includes a contrast agent injection unit 331 formed
of, for example, a syringe and injects a contrast agent into a
blood vessel of the patient or the like, an injection drive unit
332 which drives the injection operation of the contrast agent
injection unit 31, a control unit 333 that controls the operation
of the injection drive unit 332, and a contrast agent injection
detection sensor unit 334 that detects whether or not the contrast
agent is being injected into a blood vessel or the like of the
patient from the contrast agent injection apparatus 330.
[0241] The injection drive unit 332 moves, for example, the piston
of the syringe of the contrast agent injection unit 331 and is
formed of a power means, such as an air pressure, motor, or
hydraulic pressure.
[0242] The contrast agent injection detection sensor unit 334
includes a sensor for detecting that the contrast agent is
discharged from the contrast agent injection unit 331. Then, the
contrast agent injection detection sensor unit 334 outputs a
contrast agent detection signal to the control unit 314 of the
radiation image capturing apparatus 310.
[0243] The radiation exposure dose obtaining apparatus 340 includes
a contrast agent frame identification unit 341 that identifies a
radiation image signal of a frame which includes an image signal of
an image of a contrast agent as a contrast agent frame from the
radiation image signal of each frame read out from the radiation
image storage unit 313 of the radiation image capturing apparatus
310, and a radiation exposure dose obtaining unit 342 that obtains
a radiation exposure dose of the patient based on a signal
evaluation value of a radiation image signals of each frame read
out from the radiation image storage unit 313 of the radiation
image capturing apparatus 310. Operations of the contrast agent
frame identification unit 341 and the radiation exposure dose
obtaining unit 342 will be described later in detail.
[0244] The radiation exposure dose management apparatus 350 stores
the radiation exposure dose obtained by the radiation exposure dose
obtaining apparatus 340 and manages the radiation exposure dose for
each patient.
[0245] The system control apparatus 360 outputs control signals to
the radiation image capturing apparatus 310, the radiation image
display apparatus 320, the contrast agent injection apparatus 330,
the radiation exposure dose obtaining apparatus 340, and the
radiation exposure dose management apparatus 350 to control the
operations thereof and at the same time performs input/output
signal control between these apparatuses. The system control
apparatus 360 is provided with an input unit 370 which receives an
instruction input and other inputs, such as image capturing
conditions, patient ID information and the like, from the user. The
input information received by the input unit 370 is outputted to
each apparatus by the system control apparatus 360 as required.
[0246] An operation of the radiation image capturing system of the
present embodiment will now be described with reference to the
flowchart of FIG. 14.
[0247] First, a patient, the subject of the image capturing, is
placed on an image capturing platform or the like provided in the
radiation image capturing apparatus 310 and the patient is put into
position (S310).
[0248] Then, ID information of the image capturing target patient
and an image capturing condition are inputted by the user through
the input unit 370 and the patient ID information is registered in
the radiation exposure dose management apparatus 350 while the
image capturing condition is set to the control unit 314 of the
radiation image capturing apparatus 310 (S312). The image capturing
condition may include a tube voltage, tube current, and application
time in order to apply an appropriate dose of radiation to an image
capturing region of the patient, as well as a frame rate for
capturing a fluoroscopic image. As for the frame rate for capturing
the fluoroscopic image, for example, a frame rate of 5 fps to 60
fps is set.
[0249] Next, an instruction to start fluoroscopic image capturing
of the patient is inputted by the user through the input unit 370
and in response to the input, a control signal is outputted from
the system control apparatus 360 to the radiation image capturing
apparatus 310 to capture a fluoroscopic image, and the radiation
image capturing apparatus 310 starts fluoroscopic image capturing
according to the inputted control signal (S314).
[0250] More specifically, the X-ray tube of the radiation
application unit 311 is controlled based on the inputted imaging
condition and a predetermined dose of radiation is applied toward
the patient intermittently at a predetermined frame rate.
[0251] Then, radiation transmitted through the patient is applied
to the radiation image detector 312 and subjected to a
photoelectrical conversion in the radiation image detector 312 and
accumulated therein as a charge signal.
[0252] Thereafter, each time the application of radiation for each
frame is ended, the charge signal accumulated in the radiation
image detector 312 is read out by the control unit 314, then
converted to a digital signal by an A/D converter (not shown), and
stored in the radiation image storage unit 313.
[0253] FIG. 15 is a timing chart illustrating the application
timing of radiation from the X-ray tube of the radiation
application unit 311 and the charge accumulation timing of the
radiation image detector 312. The period during which no charge
accumulation is performed in the radiation image detector 312
(accumulation OFF period) is a period for reading out a charge
signal from the radiation image detector 312.
[0254] The repeated performance of radiation application by the
X-ray tube and the radiation image recording and reading in the
radiation image detector 312 at a predetermined frame rate in the
manner described above causes the radiation image signal of each
frame to be sequentially stored in the radiation image storage unit
313.
[0255] Then, the radiation image signals of each frame stored in
the radiation image storage apparatus 313 are sequentially read out
and outputted to the radiation image display apparatus 320. The
radiation image display apparatus 320 sequentially generates
display control signals based on the inputted radiation image
signals of each frame and sequentially outputs the display control
signals to the monitor to display a fluoroscopic image of the
patient as a moving picture (S316). It is assumed here that the
radiation image signals with respect each frame stored in the
radiation image storage unit 313 will remain un-erased in the
radiation image storage unit 313 after being read out.
[0256] Here, if the user desires to observe a contrast agent image,
such as a blood vessel or the like, while the fluoroscopic image
capturing and display are performed in the manner described above,
a contrast agent injection instruction is inputted through the
input unit 370 (S318).
[0257] When the contrast agent injection instruction is inputted
through the input unit 370, a control signal is outputted from the
system control apparatus 360 to the contrast agent injection
apparatus 330. The contrast agent injection apparatus 330 starts
contrast agent injection based on the inputted control signal. More
specifically, the contrast agent injection unit 331 is driven by
the injection drive unit 332 and a predetermined amount of contrast
agent is discharged from the contrast agent injection unit 331.
[0258] Here, the contrast agent injection detection sensor unit 334
provided in the contrast agent injection apparatus 330 detects that
the contrast agent is discharged and a detection signal is
outputted to the control unit 314 of the radiation image capturing
apparatus 310 (S320). When the contrast agent detection signal is
inputted, the control unit 314 of the radiation image capturing
apparatus 310 appends to a radiation image signal of a frame
captured while the contrast agent detection signal is inputted
information indicating that it includes an image signal
representing an image of the contrast agent (hereinafter, referred
to as "contrast agent frame information")as header information, and
stores the radiation image signal in the radiation image storage
unit 313 with the header information (S322). More specifically, if
the contrast agent detection signal is inputted to the radiation
image capturing apparatus 310 in the timing illustrated in FIG. 15,
the contrast agent frame information is appended to the radiation
image signals of frames F1 and F2 captured while the contrast agent
is injected and stored in the radiation image storage unit 313.
[0259] Then, the radiation image signals captured while the
contrast agent is injected are also readout from the radiation
image storage unit 313 and sequentially outputted to the radiation
image display apparatus 320. The radiation image display apparatus
320 sequentially generates display control signals based on the
inputted radiation image signals, and displays radiation images
including a contrast agent image on the monitor based on the
display control signals (S324).
[0260] Then, after the discharge of the predetermined amount of
contrast agent from the contrast agent injection apparatus 330 is
completed and the contrast agent detection signal is not detected
anymore in the contrast agent injection detection sensor unit 334,
radiation image signals captured are stored in the radiation image
storage unit 313 without the contrast agent frame information being
appended, and radiation image signals with respect each frame are
read out from the radiation image storage unit 313 in the manner
described above and a fluoroscopic image is displayed on the
radiation image display apparatus 320.
[0261] Thereafter, when an instruction to end the fluoroscopic
image capturing is inputted by the user through the input unit 370,
the system control apparatus 360 outputs a control signal to the
radiation image capturing apparatus 310 to end the fluoroscopic
image capturing, and the radiation image capturing apparatus 310
ends the fluoroscopic image capturing in response to the inputted
control signal (S326).
[0262] When the fluoroscopic image capturing described above is
ended, the system control apparatus 360 reads out radiation image
signals of all frames stored in the radiation image storage unit
313 of the radiation image capturing apparatus 310 and inputs the
radiation image signals to the radiation exposure dose obtaining
apparatus 340.
[0263] Then, first, the contrast agent frame identification unit
341 identifies a radiation image signal of a frame to which
contrast agent frame information is appended from radiation image
signal of all frames and identifies the frame as a contrast agent
frame (S328).
[0264] Next, the radiation exposure dose obtaining unit 342
calculates a radiation exposure dose received by the patient during
capturing of each frame of the fluoroscopic image based on the
radiation image signals of each frame (S330). More specifically, an
E.I. (Exposure Index) is calculated as a signal evaluation value
based on the radiation image signals of each frame in the present
embodiment and based on the E.I., the radiation exposure dose is
obtained.
[0265] The E.I. is calculated in the following manner. First, a
predetermined calculation area is set in a radiation image of each
frame. The calculation area may be, for example, the entire area of
the radiation image, an area arbitrarily set by the user, an area
defined based on the imaged region information, or an area within
10% of the image size from the center of the radiation image.
Otherwise, an area except for the so-called direct exposure area
which may be obtained based on, for example, a histogram of the
radiation image or an area of 90% of the entire density width from
the central density of the radiation image may be employed.
Alternatively, a specific calculation area may be set by combining
the aforementioned conditions.
[0266] Next, a representative value V of the calculation area set
in the above is calculated. As for the representative value V, the
density value itself of the radiation image or a statistical
characteristic value obtained by modifying the density value itself
with the average value of the entire density values, median value,
mode value, or trimmed mean value may be employed. Then, based on
the representative value V, the E.I. of each frame is calculated by
the formula given below:
E.I.=C.sub.0.times.g(V),
where: [0267] g(V) : reverse calibration function; and [0268]
C.sub.0: 100Gy (constant).
[0269] Here, g(V) is a function defined based on a radiation image
obtained with the radiation quality of RQA5. The representative
value V differs in magnitude due to difference in sensitivity
arising from difference in scintillator used in the radiation image
detector or difference in the setting method of the calculation
area or the calculation method of the representative value V and
g(V) is a function to normalize the differences. That is, if RQA5
radiation is received by any type of radiation image detector by
the same radiation dose, the E.I. will become nearly the same
value. A radiation exposure dose received by the patient during
capturing of each frame is obtained using the E.I. calculated in
the radiation exposure dose obtaining unit 342 based on the
radiation image signals of each frame in the manner described
above. As for the method of obtaining the radiation exposure dose
using the E.I., for example, a function which defines these
relationships or a lookup table may be set in advance.
[0270] The graph at the bottom of FIG. 15 illustrates the radiation
exposure dose obtained in the manner described above for each frame
connected by a line and the horizontal axis of the graph indicates
the frame number from the start of imaging.
[0271] Here, in the case where a contrast agent is injected and a
contrast agent image is captured in the middle of the fluoroscopic
image capturing as described above, the radiation applied to the
patient is absorbed by the contrast agent before reaching the
radiation image detector 312. Therefore, if a radiation exposure
dose is calculated based on the radiation image signal of the
contrast agent frame, the calculated value will become smaller than
that actually received by the patient. More specifically, if a
radiation exposure dose is calculated based on the radiation image
signals of frames F1, F2 illustrated in FIG. 15, the calculated
radiation exposure dose will become smaller than the actual value
(estimated value close to the line connecting the frames
immediately preceding and following the frames F1, F2 which
includes a contrast agent image).
[0272] Consequently, in the present embodiment, a value corrected
by linear interpolation using a radiation exposure dose of a frame
other than a contrast agent frame immediately preceding the
contrast agent frame and a radiation exposure dose of a frame other
than a contrast agent frame immediately following the contrast
agent frame is used. More specifically, linear interpolation is
performed using radiation exposure doses calculated based on
radiation image signals of the frames captured immediately before
and after the frames F1, F2 which includes a contrast agent image,
as illustrated in the graph of FIG. 15, and radiation exposure
doses at the imaging timing of the contrast agent frames F1, F2 on
the linear line are obtained, whereby radiation exposure doses of
the patient during the capturing of the contrast agent frames F1,
F2 are obtained.
[0273] Then, the radiation exposure dose obtaining unit 342
calculates a total radiation exposure dose of the subject
throughout the continuous radiological imaging by adding radiation
exposure doses of all frames.
[0274] The total radiation exposure dose obtained in the radiation
exposure dose obtaining unit 342 in the manner described above is
inputted to the radiation exposure dose management apparatus 350,
and the radiation exposure dose management apparatus 350 registers
the total radiation exposure dose with the ID information of the
patient inputted in advance (S332). Then, the radiation exposure
dose management apparatus 350 displays the registered total
radiation exposure dose with the ID information of the patient as
required or calculates a cumulative radiation exposure dose from
the past for a particular patient and displays a warning message if
the cumulative radiation exposure dose is greater than a
predetermined specified value.
[0275] According to the radiation image capturing system of the
present embodiment, a frame which includes an image signal
representing an image of a contrast agent is identified as a
contrast agent frame from the radiation image signal of each frame
and, for a radiation exposure dose of a contrast agent image, a
value corrected by linear interpolation using a radiation exposure
dose of a frame other than a contrast agent frame immediately
preceding the contrast agent frame and a radiation exposure dose of
a frame other than a contrast agent frame immediately following the
contrast agent frame is used. This allows more accurate radiation
exposure dose of a subject which takes into account the inclusion
of an image of a contrast agent in the radiation image to be
obtained.
[0276] So far, a preferred embodiment of the fourth radiation
exposure dose obtaining apparatus of the present invention has been
described, but the fourth radiation exposure dose obtaining
apparatus of the present invention is not limited to the
aforementioned embodiment. For example, a contrast agent frame may
be identified by any method other than the aforementioned method
that uses the contrast agent injection detection sensor described
above, such as a method in which a contrast agent injection time
obtaining unit is provided and injection start and end time of the
contrast agent are obtained by the contrast agent injection time
obtaining unit and a contrast agent frame is obtained based on the
time information, a method which identifies a frame whose signal
evaluation value is within a predetermined range and differs from
that of a frame other than the contrast agent from as a contrast
agent frame without using these sensors, or the like.
[0277] Further, the radiation exposure dose obtaining apparatus is
implemented as an independent apparatus in the embodiment described
above, but it may be implemented in any other form, such as being
incorporated in the other apparatus, such as the radiation image
capturing apparatus, as a part thereof. More specifically, it may
be provided in a console which includes the system control
apparatus 360 or in the radiation image capturing apparatus 310.
Further, in the case where the radiation image detector 312 is
accommodated in a portable electronic cassette, and hardware of
electronic circuits, such as LST (Large Scale Integration),
hardware of programmable electronic circuits, such as PLD
(Programmable Logic Device) FPGA (Field-Programmable Gate Array),
and the like are accommodated in the electronic cassette, the
identification of a contrast agent frame and acquisition of
radiation exposure dose may be performed by the hardware. Such
arrangement allows pursuit of more real time implementation.
[0278] Further, it should be appreciated that, other than the first
to fourth embodiment described above, various modifications and
alterations may be made without departing from the spirit of the
present invention.
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